I want to work with mentally handicapped children, what do I need to go to college for?

Child development or Deaf studies/ASL.

Also, google “American Humanics” and get involved with them when you are a sophomore or junior.

in highschool?

Special Ed?

@Aster yes, prefferably.

Special ed, deaf education and speech therapy are generally considered separate career paths. If you’re really into the language part of it, you should look into getting an education in language and speech pathology.
http://careerplanning.about.com/od/occupations/p/speech_path.htm

I got my bachelor’s in Education and specialized in special education.(That prepared me mostly for work in a resource room or self contained classroom) I think you can get other specializations too, like working with children who are autistic. I agree with @GeorgeGee that there are different paths as well. I suggest talking to a guidance counselor or a career counselor.

Thought I would mention that deafness is not an intellectual impairment… good luck with your career choice @Rayvin14 :)

@Adagio Well, I know its not an intellectual impairment, but I would like to be able to work with handicapped children, or be a speech therapist for the deaf. I just cant decide which yet! :)