Maria:
Each Moderate resort's rooms are the same size and all use buses to the theme parks, so it comes down to theme and pool for my recommendation.
If you have boys, I'd consider a preferred Pirate room at
Caribbean Beach Resort. The two beds that are shaped like boats, along with the plank carpet, will make the trip memorable. But that doesn't compare to the pool area with a water play station for your 4-year-old and a Spanish-fort-themed slide and play area for both to enjoy that anchors the larger pool. Its downside is the same for the other Moderates: the campus is spread out and its bus makes multiple stops which can cramp a return trip home from the parks, but if you know this going in, and enjoy the tropical feel, you're children will be tickled at the place.
Girls and boys enjoy
Port Orleans: Riverside, although the Magnolia Bend Section seems more appropriate for little girls while the Alligator Bayou area is rustic. The lush landscapes remind me of a Deluxe, but this resort's leg up is its ferry to Downtown Disney. Our family enjoyed riding in the daytime as well as seeing the lights of DTD at night. Its large pool sports a slide, and although it isn't as "new" as CBR's, my children loved it when we stayed there when they were 6, 8, and 10. You can opt for the smaller Port Orleans French Quarter if you'd prefer less walking to your room, and you can visit POR's larger pool with a 10-minute walk.
Wishing y'all a magical vacation!
Whitney