We've stayed at Sun N Fun in Bradenton, and would like to take our kids someday. It was only for one night, but I toured the grounds.
Sarasota RV Parks, Campgrounds & Camping Resorts | Sun-N-Fun
All kinds of family friendly stuff... putt putt, jumping pillow (like jumping on a bed the size of a basketball court), huge pool with dine-in movies, shuffleboard, horseshoes, crafts, tons of events daily.
I would also recommend considering spending time at places to go near New Port Richey and even farther north. Homosassa Springs State Park is a GREAT place to take the kids. It used to be a privately owned wildlife park, and the state turned it into a State Park. Lots of native animals to see, including one non-native animal (a hippo). It is also a recovery center for injured manatee. Very cool place, one of our favorite cities to go.
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There is also Weeki Wachee Springs State Park where you can see the mermaids. Will probably be too cold for the water park, but there is still lots to see and do there like a river boat cruise or canoeing/kayaking the beautiful water.
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