Hi Arlene! Yes, a section of the Animal Kingdom is devoted just to dinosaurs called DinoLand USA. Your son will be able to ride TriceraTop Spin (think Dumbo with dinosaurs) and play in The Boneyard, which has a "dino dig" in it as well as a large play area with a smaller area for toddlers. Also, at Epcot, dinosaurs are part of the Universe of Energy ride. At Downtown Disney, a new restaurant is being built called TRex, which is like the Rainforest Cafe but all about dinosaurs!
For trains, the train ride around the Magic Kingdom is fun and relaxing. While at Epcot, make sure and stop outside the Germany pavilion where a miniature train makes its way around a small German village.
For planes, this is a bit trickier. Soarin is a wonderful ride that recreates flying over the coast of California, but there is a minimum height of 40" required. You and your son may enjoy Goofy's Barnstormer at the Magic Kingdom; it is a child friendly "roller coaster" with guests riding in Goofy's planes. It does have a 35" height requirement. I hope this helps with your planning - Kara