It is common for children and adolescents with Down Syndome to show many different forms of self-stimulator behavior, includig masturbation. It is important for you and the other other adults involved in your son's care to begin to help him to distinguish between appropriate and inappropriate forms of stimulation and situations in which this behavior is appropriate. Allowing him to touch himself in public will limit his opportunity to be included in certain activities and settings and may limit opportunities for appropriate social interaction. If he rubs himself in public, either against an object or person, interrupt this behavior and direct him toward an appropriate activity. More importantly, try to be sure that there is some appropriate alternative easily available to him at all times. If there is nothing appropriate to do he will find some way to stimulate himself. If you have any concerns about his interactions with children please do supervise him carefully and seek in-person professional consultation.