L.C.
Hi R.,
We live in LA too and had the same conversation when we went to Florida last January. My son is 7 though. We did not go to the Magic Kingdom since it is essentially the same as Disneyland in LA - expect for a few minor differences. If you only have one day I would go to the Animal Kingdom. It was great! Much nicer than I expected. Much nicer that San Diego Wild Animal Park. For really little kids this is the best option. Lots of animals, some nice shows for little kids (I think we saw a Finding Nemo show) and some rides and arcade games for little kids. There is also a "Safari" ride. We loved Epcot too but little kids won't get it. 1/2 of Epcot is made up of Pavillions from different countries. The other half are rides that better suit older kids and that talk about techology and give the kids hands on opportunties. My son is 7 and he loved Epcot the best but he's really into science so it was perfect for him. I think Animal Kingdom would be a great experience for you and your kids.
Hope this helps!