Hi Sabrina!
I'm assuming you will actually be in the parks on the 23rd and 28th of July, so I suggest the following:
- Monday: Epcot
- Tuesday: Hollywood Studios
- Wednesday: Magic Kingdom
- Thursday: Water Park?
- Friday: Animal Kingdom
- Saturday: Magic Kingdom
While many people start off with the Magic Kingdom, I suggest saving that for your son's birthday on Wednesday. I also suggest a water park on Thursday, but it depends on how much your son likes the water. Both of my children enjoyed Typhoon Lagoon (mostly the kids' area and the lazy river) at that age, but they grew up around water.
I think a special birthday surprise is breakfast at the Crystal Palace, especially if your son like Winnie the Pooh, and then dinner at Chef Mickey's in the Contemporary. It's easy to get to and from the Contemporary from the Magic Kingdom via the monorail. Thus you could have dinner there and then return to the Magic Kingdom afterward.
Be sure to make Advance Dining Reservations (ADRs) for any Table Service restaurants you want to try. ADRs can be made online or by calling (407) WDW-DINE and can be made 180 days in advance!
Enjoy planning your magical Walt Disney World Resort vacation!