We've done the Eastern twice, DS was 6 (almost 7) and 9 on the cruises, we've loved it (though I would not repeat going to St. john's, which gets kinda schleppy with two taxis and a boat each way, a lot of travelling time for a little one--just go to one of St. Thomas' wonderful beaches--Magan's Beach gorgeous and calm for little ones), and even if not in the Club/Lab he has found friends and hung out and found things to do. And treats to eat! And St. Martin is so easy to just take the water taxi to great bay beach and be in view of the ship if you need to go back for lunch or anything. Or Orient Beach was gorgeous and a very easy cab ride away--but a bit enlightening even at the end of the beach away from the au natural crowd.
We're doing a special Western next year, going to try one fewer sea day, two stops at CC, and a bit of Mexico with our then-10 yr old, but can't compare until then.