My kids LOVE the splash pads. My oldest is sad he just outgrew them; on our October trip, he was at the sweet spot where he was short enough barefoot for the spraygrounds with slides, but tall enough with shoes on to ride Tron. So we've been to a lot of Disney splashgrounds over the past 6 or 7 years.
My kids' current favorite: Poly ...but there are hidden alcoves and it is pretty expansive, so I would have been nervous had they been younger (they were ages 4 and 7 when we were there). But they love it because it is so expansive and it has a tunnel slide.
When my son was younger, his favorite was Fort Wilderness. He loved that little sprayground. Cons to there are that the bathrooms by the pool don't have showers and the cabins won't have laundry in them. The SSR splashground is very similar, so SSR might be a better choice.
SSR has the splashground by Paddock Pool, zero entry and a toddler slide at High Rock Springs (plus a basic splashpad, but my kids were sad that the Donald Duck statue had been removed from it), the Congress Park pool was just a pool but the dry playground was nearby, and a really cute horse-themed sprayground at the Grandstand pool (which also had limited food options...we ate lunch there one day). I think for that age range I would recommend SSR. Only con is no sand to play in...though as a parent, I sometimes see that as a pro, not con, that the SSR playground is not in sand like some of the others.
I would not recommend Old Key West for kids in the sprayground stage because all they have is a basic wading pool.
Grand Floridian has an adorable splashground and I wish we had been there when it was warmer. We were there shortly before X-mas 2022 and lasted maybe 15 minutes before going to the big pool, which was warmer.
Next trip we will be at AKL. The water playground looks cute, but if my son was younger, he would be disappointed that there are no kid-sized waterslides like at the SSR/VGF/Ft. W/Poly/POFQ/CBR splashgrounds. While CBR isn't
DVC, it's my kids' 2nd favorite pool after the Poly.