My 5 year-old daughter has been to WDW four times and has had to watch whilst her big sister (she's now 7) went on Splash, ToT & Test Track. I've just measured her and she's now big enough (with trainers on) to go. She's jumping about the place at the moment and we're not going back until next year! She can't wait.
Those are some awesome rides! She will like them a lot!