From Pierson v. Pierson (Fla. Ct. App. Aug. 18, 2014) (some paragraph breaks added):

[W]e agree with the father that the trial court abused its discretion in granting [the mother] … ultimate authority over the children’s religious upbringing and in prohibiting the father from “doing anything in front of the children or around the children” that “conflicts with the Catholic religion.” …

The parties have three minor children who were born in 2003, 2005, and 2009. While the parties’ marriage was intact, the children were raised in the mother’s religion of Catholicism. The mother petitioned for the dissolution of her marriage to the father in 2012. During the parties’ separation, the father became a Jehovah’s Witness. As a result, one of the issues to be decided in the proceedings was the children’s religious training following the dissolution.

During the hearing on the petition, the mother called Dr. Charlotte Chadik, the Director of Family Ministries of the mother’s church and a licensed psychotherapist. Dr. Chadik served as the “communication link” between church teachers and parents.

When asked whether she was made aware of problems that the parties’ oldest son was having in Sunday School, she testified that the third grade Sunday School teacher reported to her about the child’s “behavior one day,” which included telling the teacher and students that the music they were listening to was wrong, that priests were bad, that he was going to grow up to be a Jehovah’s Witness minister, that the Bible they were using was wrong, and that there was no Heaven. When asked during the hearing if she had an objection to the father exposing the children to his beliefs, the mother expressed her concern that it was “confusing” for the children.

In the amended judgment, the trial court noted Dr. Chadik’s testimony and found the “beginnings of a substantial emotional problem” in the parties’ oldest son, who was then nine years of age, as a result of “being immersed in and exposed to two religions simultaneously.” Based upon the “demonstrated harm,” the court ordered “shared parental responsibility” with the mother having the “ultimate” religious decision-making authority for the children. The court prohibited the father “from doing anything in front of the children or around the children that disparages or conflicts with the Catholic religion.” It also prohibited the mother from disparaging the father’s religious beliefs in front of the children….

Restrictions upon a noncustodial parent’s right to expose his or her child to his or her religious beliefs have consistently been overturned in the absence of a clear, affirmative showing that the religious activities at issue will be harmful to the child…. “[A]lowing a court to choose one parent’s religious beliefs and practices over another’s, in the absence of a clear showing of harm to the child, would violate the [F]irst [A]mendment [of the United States Constitution].” …

In the present case, while Dr. Chadik testified about what she was told regarding the parties’ oldest son’s behavior in one Sunday School class, she did not testify in her capacity as a psychotherapist. There was no evidence presented that Dr. Chadik or any other professional ever spoke to or evaluated the child. Nor was there any evidence presented that the parties’ two younger children were harmed by their exposure to the father’s religious beliefs or activities. While the mother’s concern that exposure to two different religions could confuse the children may be reasonable, neither that concern nor the evidence presented below established the requisite showing of harm to grant the mother ultimate religious decision-making authority for the children and to restrict the father from “doing anything in front of the children or around the children that … conflicts with the Catholic religion.” …

[T]he only evidence in this case that was presented below in support of the religious restriction pertained to one incident involving one of the three children. Because the evidence did not establish the harm necessary to award the mother ultimate religious decision-making authority and to restrict the father from “doing anything” in front of or around the children that “conflicts” with the Catholic religion, we reverse the amended judgment accordingly.

[Footnote:] We find no error in the trial court’s directive that neither parent disparage the other parent’s religion in front of the children.

For more on this issue — and on child custody speech restrictions more generally, whether they deal with religion or anything else — check out Parent-Child Speech and Child Custody Speech Restrictions, 81 NYU L. Rev. 631 (2006).

UPDATE: Some of the comments lead me to post this excerpt from my article, where I explain how I think the law should deal with such matters; note that this is just an excerpt, and will seem pretty conclusory in the absence of the arguments earlier in the article — if you’re really interested in the subject, you might have a look at the article more broadly (long as it is):

C. Restrictions on Speech That Undermines the Child’s Relationship with the Other Parent

Restrictions on non-ideological speech (“your mother is a whore” or “your father’s new wife is a whore”) justified by the interest in protecting the child’s relationship with the other parent should generally be constitutional. They seem unlikely to materially interfere with public debate, and likely to protect both the children’s best interests and the other parent’s rights; and if framed as injunctions, they can be crafted in a way that is clear enough to comply with the void-for-vagueness doctrine. The restrictions do burden parents’ desire to express themselves, and may deny information to the children; but, as Part II.A.2 argued, these concerns shouldn’t play as much of a role here as they do with adult speech.

The restrictions should, however, be tailored to allow ideological teachings that don’t expressly mention the other parent, even when the ideology condemns some behavior that the other parent happens to engage in or some beliefs that he holds. Restricting such ideological teachings would have some effect on public debate; and it would generally require courts to discriminate among viewpoints, for instance letting parents criticize racists even when the other parent is a racist, but not letting them criticize Catholics when the other parent is Catholic.

Moreover, while such restrictions may protect the other parent’s relationship with the children, it seems to me (though here I am less certain) that narrower restrictions may do the job well enough. We as adults recognize that people may have traits or beliefs we disapprove of, yet still be generally good people. Children can likewise be taught this, and often are taught this.

Many a mother who genuinely loves her husband, but disapproves of his racism, may teach her children that racism is bad, and may even feel more of a need to do so precisely because the children are especially likely to learn otherwise by looking at her husband’s actions. When the children ask her if this means their father is bad, too, she can tell them that he’s a good person who has some bad habits, like all of us do; and that the kids should emulate his many good traits but not his few bad ones. Likewise, a father who says, “anyone who doesn’t embrace Jesus will go to Hell,” “homosexuality is a sin,” “racists are bad people,” or “religion is superstitious folly,” and whose children then ask, “Does that mean mommy will go to Hell / is a sinner / is a bad person / is stupid?,” can respond with something positive: “Mommy is a good person who loves you very much, and while she’s wrong about this, I’m sure she’ll come to the right path eventually.”

Such subtle requirements may not be easy to set forth or to enforce, especially when the family is split and each parent is not emotionally inclined to defend the other parent to the children. A flat “Don’t say anything that is expressly or implicitly critical of the other parent” or “Don’t express any anti-homosexual views” may seem relatively enforceable. A more nuanced “Don’t make any non-ideological statements critical of the other parent, don’t use the other parent as an example for any of your ideological teachings, and if the children ask you whether the other parent is bad, tell them ‘no’ and sound credible” may seem like a recipe for endless future debates. Nonetheless, it seems to me that on balance courts should try to narrow their injunctions as much as possible, rather than completely banning parents from teaching their moral views whenever those views might cast the other parent in a bad light.

Here, there may be more room for looking at whether the speech is likely to cause serious psychological harm. The harm inquiry’s drawbacks still remain, but they may be less dangerous here: Because these restrictions are less likely to systematically suppress some ideology, errors in determining harm will be less costly. But I still think that on balance the harm inquiry is too flawed to be helpful even here.

D. Restrictions on Speech That Contradicts the Custodial Parent’s Religious Teachings

Restrictions on the teaching of conflicting religions to children are unlikely to dramatically affect public debate, if they are applied evenhandedly. Their chief effects are likely (1) to strengthen relatively devout religious ideologies, by making it more likely that children will learn such ideologies from their parents with no interference from the other parent, and (2) to correspondingly weaken more agnostic, latitudinarian, or doubting approaches to religion, since these approaches seem likely to flow (often without the parents’ so intending) from the teaching of rival religious views to children. But these effects seem likely to be quite modest.

Such restrictions, however, pose Establishment Clause problems, because they require courts to determine which teachings are religiously incompatible enough with the custodial parent’s. For instance, an order that a father not “expose or permit himself or any other person to expose the minor children of the parties to any religious practices or teachings that are inconsistent with the [Catholic] religious teachings espoused by the [mother]” requires a court to decide which teachings are “inconsistent” with Catholicism — a question that may often be hotly contested, and that can only be resolved by making judgments about religious doctrine, something courts are generally barred from doing.

Similar problems arise with judgments that the visiting parent may not, for instance, teach children Catholicism when the custodial parent teaches them Judaism, based on “judicial notice” that “the practice of Judaism and that of Roman Catholicism cannot be squared. To accept and adhere to the teachings of one necessarily requires a rejection of the other.”

Doubtless most Jews and Catholics would agree that one can’t simultaneously adhere to all the teachings of Judaism and all of Catholicism. But few Jews adhere to all the teachings of Judaism (or even of the particular type of Judaism that they see themselves as following), and few Catholics adhere to all the teachings of Catholicism. They focus on what they think are the most important tenets of the religion, and feel free to depart from those tenets that they see as unimportant.

And the question whether the most important parts of Judaism and the most important parts of Catholicism can “be squared,” in the sense that a person can find spiritual meaning in both, will likely yield much less consensus. This may help explain why the appellate court in the case I quoted rejected the order, concluding that “the extent to which Judaism may be ‘reconcilable’ with Christianity involves theological and philosophical issues far beyond our ken or cognizance. It would be impermissible for [a court] to determine orthodoxy in either religion, let alone . . . compare orthodox beliefs in one to those of the other to make a judicial determination of the reconcilability of Judaism and Christianity or of any other religions.”

Moreover, such restrictions do not seem inherently necessary to prevent harm to the child, or even to serve the child’s best interests. As Part II.B.4 discussed, it’s plausible that children may benefit from being taught just one religion — but it’s also plausible that they may benefit from being taught two. One’s judgments about this likely turn on how valuable one thinks faith is relative to doubt, a subject that civil courts are barred by the Establishment Clause from considering.

Even if one focuses purely on the child’s secular interests, by asking whether a child is likely to feel confused by rival teachings or to see them as undermining his parents’ authority, the matter remains unclear. Learning to deal with confusion caused by contradictory views from authoritative sources may itself be valuable. There seems to me to be little reason to assume, as a categorical matter, that such conflicting teachings are against the child’s best interests. And there’s also reason to doubt that a judge can reliably make such a judgment in any individual case.

Nor is there reason to have much confidence in a test that allows such orders only if there’s evidence of likely psychological harm. Such evidence, as I’ve argued above, is likely to be very hard for courts to accurately evaluate.

And where such necessarily subjective judgments are involved, even a well-intentioned judge may find more likelihood of psychological harm where an unpopular or unfamiliar religion is involved than where a more common one is involved. Many mainstream religions require some tradeoff of present pleasure for future happiness (in this life or the next); I suspect, however, that few courts would find psychological harm from being taught to embrace those tradeoffs. Likewise, many mainstream religions teach doctrines or bloody stories — about damnation, divine wrath, sex, and so on — that can make children fearful or confused; but I suspect that few courts would find psychological harm from such teachings, even if the children seem upset by them. What counts as “psychological harm” and what doesn’t, even when one limits the harm to that which supposedly flows from disagreement between two religions, is thus likely to turn on intuitive judgments that are particularly likely to be influenced by sympathy or hostility to one or the other faith.