Anyway, as others have said the park hopper option isn't probably needed. You can get the "Base ticket" and if you only get a 3 day ticket, it's the same cost at The Disney Store at MOA as it would be at the gate since the savings only start at 4-day tickets.
While you are experienced with Disneyland, you're going with the kids. I would suggest Magic Kingdom for sure. While you've seen a lot of Disneyland and Magic Kingdom is similiar, it's still quite new to him and very new to baby!
Animal Kingdom is also nice, especially if you enjoy animals. Remember, it's not a zoo, but if he enjoys the Minnesota Zoo or Como Zoo this will be a lot of fun for him. Add in the number of shows, including the new Nemo show and I'm sure you'll have a blast.
The third day would then leave you picking between Epcot or the Disney-MGM Studios. Epcot has "kid cot" activities all over, the newly re-done Living Seas - with Nemo and Friends (attraction, turtle talk, etc.) There is also a nice character meet and greet, Character connection where the wait is minimal for a number of classic characters, Imagination with Figment, Soarin' at the Land, and others. (Remember to take in height requirements for some attractions.) The Disney-MGM Studios also has a lot of characters to see, but has a lot of shows. Shows include Muppet*Vision 3D, Voyage of the Little Mermaid, Playhouse Disney, Beauty and the Beast, Indiana Jones Epic Stunt, and Lights, Motors, Action! There's also the Honey I Shrunk the Kids play area, Great Movie Ride, and Back Lot Tour. However, some things would scare the baby and might scare the 4 year old. You know him best.
One tip is to learn of the Rider Switch Program. Ask a Cast Member at any height restriction attraction for details. You can't miss out on Everest now, can you?
Just a few ideas. Have fun. Enjoy your trip and best of luck on that 26 hour drive!!