Hi, Stephanie! Taking your family to WDW for the first time is so magical! You must be very excited.
For a 4 year old boy, you might want to consider
Caribbean Beach. This Moderate Resort has Pirate Themed rooms (yep, even pirate ship beds!), several pools around the resort, and the main pool area is a blast with a splash area, pirate ship at the pool and even a slide. There is a nice food court, sandy beaches (sorry, so swimming in the lake) and walking paths around the resort.
If you are considering a Value Resort, you son might like
All-Star Sports. This has always been a favorite for my kids. There is a fun sports theme throughout the resort, a huge pool, game room, food court, and just a bunch of fun for kids.
Good luck planning your vacation!