See if you can take a look at some photos from T-Rex, there were some reports of little kids being scared. I think the kids reported were younger than 5 though.
We love RFC! Haven't been to the one at WDW (will be 12-24 though!), but go to the one at Sawgrass Mills in Sunrise/Ft. Lauderdale whenever we are in the States. The kids love to see all the animals and the "thunderstorms" are pretty cool. Food is pretty good too with large portions.