Do I need to go to special classes as a parent of a disabled child?

Might help. "need" is a loaded word, but many parents find it useful to gain specific knowledge about their child's disability, perhaps talk with other parents facing similar issues, and quite likely learning proven techniques for dealing with road blocks your child may face. Often, this is a learning process that will need refreshing as the child ages and new issues arise.
No but learn a lot. No you don't need to go to special classes but you should try to learn as much as possible from many sources. Support groups (check with your local hospital and doctor's office), disease specific associations, the internet (as long as it is a reputable, physician-reviewed website), etc.