Liz:
With the ages of your children, there's no reason why you shouldn't visit all four of the theme parks. In fact, I would recommend adding one more day to your tickets cost about $5 per person) so you can make the most of your arrival day.
When planning your park days, begin and end your vacation with a bang, literally. Study the
park calendar and decide which parks will host a fireworks show because Hollywood Studios doesn't show Fantasmic every night nor does Magic Kingdom hold an evening parade daily. Our family typically visits Magic Kingdom or Epcot the first night because those are the parks we want to visit twice.
ANOTHER TIP: If you can, choose the smaller parks (DHS & MK) for the weekdays when crowds are generally smaller and the larger parks (Epcot & Animal Kingdom) for the weekend. Once you decide on your parks, you can choose your restaurants.
Schedule one table service meal a day, otherwise you'll spend all your time eating. Base those choices on your parks or nearby resorts. For example, we leave Magic Kingdom to eat at nearby Chef Mickey's and Ohana. These two top my list for you to consider, also. Other recommendations: a princess meal at Akershus because your son isn't too old yet to think it's uncool. Dinner there makes the most of the dining plan. Another fun choice for this park: Teppan Edo or Biergarten, especially if you have picky eaters.
DINING TIP: On the day you visit Animal Kingdom, save your table dining for a restaurant at a resort. I'm ambivalent to the dining choices there, and I think it would be fun to visit Whispering Canyon at Wilderness Lodge or 1900 Park Fare to see Cinderella, the Prince and my favorites: the wicked step-mother and step-sisters.
Wishing y'all a magical vacation!
Whitney