Eagle Academy Public Charter School in Washington, D.C., issued this message to parents after increasing concerns about students arriving to class smelling of marijuana. (Eagle Academy Public Charter School)

Cassandra Pinkney, the founder of a charter school in Southeast Washington, makes video messages for parents about how to prepare their children for school: Establish a bed-time routine, read with them, eat healthy food, and, with the city’s relaxed position on marijuana use, do not smoke pot around them.

In a “fireside chat” titled “marijuana and your student,” the director of Eagle Academy Public Charter School, which enrolls children in preschool through third grade, told parents that, even though the District has legalized marijuana, it’s not safe to expose children to the drug. Even second-hand smoke can affect their emotional state and attentiveness in school, she said.

“If you were drinking in your home and your child went to reach for an alcoholic drink, you would say, ‘No don’t do that, that’s not for you,’ ” she said in the message. “A child has no choice from inhaling the smoke of a marijuana cigarette, and so you are exposing your child to dangers and things that they are not able to handle.”

As more states have moved to legalize marijuana for medical and recreational use in recent years, there is limited research about its effects on children.

Neuroscientists have shown that marijuana exposure can affect the developing brain. Teenagers and children who use it can end up with learning difficulties and are more likely to become habitual users.

Currently, there is “insufficient evidence” to show whether second-hand smoke exposure can cause children to become high, said Judith Shlay, a doctor and associate director of Denver Public Health, who is part of a committee of medical researchers monitoring health concerns related to marijuana in Colorado, where it is legal for adult use.

The only study related to the effects of second-hand smoke exposure that the committee found focused on adults. It showed “limited evidence” that adults exposed to second-hand smoke experience an increase in heart rate following exposure to marijuana smoke for one hour in an unventilated space.

Because the federal government considers marijuana an illegal drug, there have not been extensive research efforts, Shlay said.

“I tell parents, ‘Your child has one brain,’ ” she said. “ ‘You want it to develop as best as it possibly can.’ ”

Pinkney said her concerns about the effects of second-hand smoke come from her experience as an educator over many years working with families in high-poverty communities where marijuana use is common. She has seen children arrive at school smelling of marijuana and exhibiting symptoms.

“Sometimes when kids come in, they are crying, they may not be cooperative,” she said. “They may have a feeling of being out of control but can’t explain it or articulate it.”

It doesn’t happen often, she said, but when it does, it helps to get them into a room where they feel safe and can calm down. “Have them color,” she said. “They can talk it out and work it out.”

Legalization of the drug for recreational use, which went into effect in the District early this year, gave her a reason to talk to parents about it.

Ashley Watkins, a social worker at Eagle, which has campuses in wards 6 and 8, said it’s hard to know for sure if a child is under the influence of marijuana.

She recalled one instance when a first grade student was complaining of a headache, and told the nurse that her dad was smoking something that “smelled funny” in the car.

A more common concern, she said, is parents coming to pick up their children and appearing to be under the influence. Rather than sending the child home, school employees have called other relatives to pick them up or driven them home personally.

She described a little boy who came to school with a large amount of cash and declared he was going to “sell weed.” When they talked to him about it, they learned that his brother was selling drugs.

Data has shown that accidental marijuana exposure has increased in other ways since it was legalized in Colorado, primarily through the consumption of “edibles” that can be marketed as candy or other sweets, Shlay said.

Hospital and emergency room visits for possible marijuana exposure by children under 9 increased significantly in the first six months that retail marijuana was legalized in Colorado. From January through June of 2014, the rate of hospitalizations for children in that age group was 26.4 per 100,000 compared to 7.6 per 100,000 in 2010 through 2013, years that only medical marijuana was commercially available.

The state’s Health Department has developed public awareness campaigns instructing parents to lock up their marijuana and keep it out of reach of children, and to instruct their children not to eat anything without permission when they are in other people’s homes.

Mindy Good, a spokeswoman for the District’s Child and Family Services Agency, said the agency gets referrals from teachers and schools when they are concerned that a child is experiencing abuse or neglect related to a parent’s drug use, but it does not track reports by individual drug type.

Anecdotally, she said, PCP is the most common, and the use of synthetic drugs is rising. The agency has not seen an increase in marijuana use or concerns since it was legalized, she said.