As a former Fantasyland CM, I would have to say it really depends on how easy it is for you to transfer your child out of their wheelchair.
Winnie the Pooh and Small World are the only two rides in Fantasyland with a wheelchair accessible car. All the other rides allow lap children, so if you can lift them out it is not a problem. On the Disabilities FAQs thread on the main page there is a list of attractions that allow you to remain in your wheelchair. To figure out just how many rides are appropriate for your child you need to take into consideration the following:
1.) Can your child transfer? This will be the number 1 determinant of the rides they can ride
2.) How fragile is your child? Can they handle a bumpy ride or do they need a smooth ride?
3.) How tall is your child? (Many rides have a height requirement)
4.) Does your child have a cognitive disability that may cause him/her to be frightened of loud noises, dark places, etc?
5.) Is your child capable of sitting in their own seat (if they can transfer) or must they remain on your lap?
At every park there is a thing called a Guidebook for Guests with Disabilities. It has all the information you will ever need. The second half is every attraction broken up by land or area with the nature of the attraction, boarding requirements, special considerations, etc. They really should give one at the entrance to anybody who enters with a wheelchair, but that almost never happens. You have to ask for them. You can get them at Guest Relations and any place that has the information sign. As a Fantasyland CM I used to keep five or six copies in my rain gear pouch to give to guests who needed it so they didn't have to go back to the front of the park, but I don't know of anybody else who did/does this.