I wrok for Universal out her ein CA and have a bit of advice- this is for anyone- but especially if your child is on the thin side...make sure thatthe lap bar or restrant doens't have too big of a gap ( so your child does not slde around too much, this could result in injury). Also make sure that your child's head is a few inches aove the lap bar and that your child does not duck down during the ride ( especially fsat rides). A common injury on theme park rides is children getting knocked around or sliding forward and hitting the lap bar. Even if a child makes the height requirment, I really think it is safer on some rides to make sure that the child is a good two inches above the height requirment. I think Kali River Rapids would be fine, since it is a fairly tame ride, witha seat belt harness. Just be sure to really carefully check out the restraints for each ride. Also, you might want to ask the attendant at each ride, why the particular height requirment was used. The reasons for the requirments vary for each ride and you may realize that it is a ride you would not want to have your child ride. Just be sure to take the time to really check things out. Have a great trip!!! - Karen