RE: Need advice - windsurfing margarita
They have a marine museum / aquarium on the island that could be fun for kids, but it's not in El Yaque. Your wife and kids could take a taxi there or something while you windsurf.
When I was in El Yaque, there were lots of kids of all ages and nationalities playing on the beach and swimming in the shallow water near shore. So if your kids like to play on beach they should be pretty happy.