Hi Keith!
I'm so excited about your first trip to Disney! Our first BIG trip was when my kids were 1 and 4, too!
First of all, yes! You can re-enter the same park without having a park-hopper! Which is awesome when you need some naps. :)
I have lots of attraction suggestions. Here are some my kids loved:
Magic Kingdom: Mickey's Philharmagic, Mad Tea Party, Country Bears and Small World
Epcot: Innoventions, Gran Fiesta Tour, Spaceship Earth and the Seas With Nemo & Friends
Hollywood Studios: Disney Junior LIVE, Muppets 3D
Animal Kingdom: Kilimanjaro Safari, Boneyard, Finding Nemo and Festival of the Lion King
Plus, all the parades and live shows! Don't forget to check out
Traveling with Little Ones for some other great suggestions!