do you tell your children's friends/parents?

We were told by our son's doctor to tell his teachers and anyone that he may be spending a lot of time with--so they would not think it was something else and do or not do something that might hurt him. We told one of our son's friends parents--who asked if they could tell their son--we said yes. Unfortunately, this friend is a little different and hyper. He has at different times mimicked a seizure or talked to our son in a bad way. He did this in the car one time and scared my husband, who yelled at him and said don't do that ever again. He has another friend that he has spent a lot of time with this summer. At this point, we have not discussed it with his mother and wonder if we should.