Children With Fetal Alcohol Syndrome?

I have a brother who had children with a woman who was using drugs. She had three children. The first of which is not my brothers. My mother adopted them when they were very young. The youngest was born with crack in her system, the middle one seems fine, and the oldest she drank alot with and I dont know what else. He is having severe problems and I am starting to wonder if he has delayed development. He is fourteen and a lot of time acts like my 5 year old. Actually my 5 year old seems more mature sometimes. He still pees in his room. He seems to have a hard time with school work and has really bad behavioral problems. The children are homeschooled also. He just does not act like a fourteen year old child. He has adhd. The youngest is ten. She also acts young for her age. She acts like she is about 6 or 7 still. She is very small for her age and she has bad behavioral problems but not as bad as the boy. My mother just thinks its a stage they are going through but I think the oldest especially needs serious help. Does anyone know what could be wrong with them or what could help them? The middle child seems fine. I dont think her mother did anything when she was pregnant with her.