Hello Darlene and thanks for bringing such an important question to the Disney Parks Moms Panel, after all nobody wants their sweet child to feel at all unwell or unnerved during their magical visit to Walt Disney World Resort.
When my own children were younger and we rode
DINOSAUR at Disney's Animal Kingdom Park together, my very youngest daughter who I believe was aged around 7 years old at the time was quite unnerved by the general perilous nature and dark atmosphere of the DINOSAUR attraction.
However I wouldn't describe the DINOSAUR attraction as fast and it isn't a rollercoaster style ride; Guests are seated in ride vehicles that resemble 4x4 style jeeps and the motion of the ride is reasonably bumpy and quite jerky, additionally I don't recall any large drops as such.
My family enjoys popping along to make new furry friends at the
Affection Section which is located in Rafiki's Planet Watch or perhaps becoming a
Wilderness Explorer like Russell from
Disney's UP! might just be the kind of fun stop you're own young Mouseketeer is looking for!
Have a great Disney day.
~ Jane