GAITHERSBURG, Md., March 22 — Stimulants like Ritalin lead a small number of children to suffer hallucinations that usually feature insects, snakes or worms, according to federal drug officials, and a panel of experts said on Wednesday that physicians and parents needed to be warned of the risk. The panel members said they hoped the warning would prevent physicians from prescribing a second drug to treat the hallucinations caused by the stimulants, which one expert estimated affect 2 to 5 of every 100 children taking them. Instead, they said, the right thing to do in such cases was to stop...