J.L.
I'm not sure where you live, but I think your little guy would LOVE Greenfield Village/Henry Ford Museum (1 yr. family membership is only $90 right now). This is a place you can go to over and over again and he'd never get bored. There is also a few sprinkler parks around (offhand, I only know of one in Canton and Dearborn Hgts). Also check out the Metroparks website, many of their parks have pools, sprinklers, or water parks inside, not to mention beaches. Hope these idea help, have fun!!