Once the person is age 18, s/he is not considered a 'child' for this purpose. There is little if anything a parent or family member can do. You have to be able to prove the person is a danger to himself or others. It is extremely frustrating! Leaving the routine of school, trying to make their own way in the world, this is often part of what tips the balance for the person, for keeping slim hold on the illness; and then, onlookers are helpless to get action.