Hi Mae,
Your family is going to love Disney's Beach Club Resort. I just recently stayed there with my family and my kids absolutely loved Stormalong Bay. We spent several afternoons and evenings there in between our theme park days. There is so much to do and since we had a 2 year old at the time, it was the perfect place for my older two to enjoy swimming and the water slide while our youngest could splash in the zero entry shallow areas and play in the sand, too.
If you feel adventurous to head to Blizzard Beach or Typhoon Lagoon, there are areas specifically for little ones with lots to offer.
Tike's Peak at Blizzard Beach and
Ketchakiddee Creek at Typhoon Lagoon are meant for kids 48 inches and under. There are small drop slides, splash areas and shallow water areas. This would be the perfect place for your little one to have a blast. The great thing is that if one of you wanted to go on a large water slide while the other parent stayed with your son, you could both take turns and still enjoy the attractions at the water parks.
Not to deter you from going to the water parks, but I, personally, like having the convenience of staying at the resort pool, especially with little ones. Since they could get quickly tired, you wouldn't have to go far to head back for a nap or to change. So, that is something to keep in mind.
Have a splashing good time whatever you choose.
~Allison L