We have stayed at the Marriott Grande Vista and Sheraton Vistana Villages, both are very very nice and kid-friendly, playgrounds, nice pools, fountains for kids. The grand vista has a water park type pool for kids with fountains and spray things. There is a kids club for age 5 and up with all kinds of activities throughout the day and family activities at night (luau show, bonfire and story telling, ice cream socials, live bands by the pool). If you can get a good rate try one of those. Aquatica is heated and stays open I believe through September/October.