THE SUPREME COURT split, 6 to 3, last Wednesday in deciding what constitutional rights a child has when committed to a mental hospital. A senator and a minister (among others) attacked the judicial nomination of Assistant Attorney General Patricia M. Wald last Monday because they think her views on the legal rights of children threaten to destroy families. Another minister - this one in Texas - spent the entire week locked in a bitter confrontation with the state government over the way he operates three "homes" for teen-agers.

In each of these controversies, both sides were arguing for what they no doubt believe to be best for children. While this is only the modern version of that age-old dispute over the best way to raise a child, the arguments now have political and policy implications as well. The children's lobby, if it can be called that, has been beating on the doors of politicians and judges demanding that the legal rights of the young be increased. Some parents have united to resist yielding up one bit of the authority over their children that has traditionally been theirs.

Most children and parents are probably caught somewhere between. Issues that once appeared hard - whether government should be empowered to intervene in family matters, even in extreme situations like child abuse or the denial of needed medical care of the refusal to send chidlren to school - have been resolved. They have been replaced by far harder issues, partly because children are maturing earlier, both physically and mentally, and partly on the basis of what we now know.

It seems unlikely, for example, that anyone would have suggested, 30 yars ago, that the government worry about the rights of a child committed to a mental hospital at the request of its parents and with the concurrence of a doctor. But a great deal has been learned since about the mistakes psychiatrists can make, the back wards of those hospitals and the desires of some parents to get rid of children who are mentally slow but not ill.

These factors suggest that the court was probably right in permitting the use of informal, nonjudicial procedures for committing those children, but wrong to permit the same kind of informality when the children were wards of the state or after they had been committed and the question was whether they could be kept in custody.

Similarly, even if Mrs. Wald went too far in advocating that children have the right to obtain medical and legal assistance on their own, make contracts and have much greater control than they now do over their own lives, her views are not beyond the realm of legitimate discussion - and disagreement. Those who think they render her unfit to be a judge have drawn a curtain over 50 years of experience and are seeking a world in which a family is properly arranged only if all authority resides in the parents and the children are totally acquiescent.

Out of controversies like these a new consensus may eventaually develop on what at least some of the rights of children should be.