Haven't done an all inclusive with kids, just without and it was at Sandals in St. Lucia and it was fantastic! It was sooooooo nice to have everything paid for up front, the only additional costs were our excursions and spending $$$$.
Their family friendly sister resorts, Beaches, is supposed to be just as good. They have resorts in the Bahamas, Jamaica and Turks and Caicos. One day when our kids are a little older we'll be taking them to one of the Beaches resorts