if you want to just hang out at the beach, then yes its worth it grab a taxi to a hotel for the beach. Just a thought, your kids might enjoy a trip out to El Morro Fort - its an old fortress that you can climb in and around. Its on the cliffs overlooking the harbor, great view of the ships coming in and out of the harbor. Its windy there , very popular kite flying place.
If you want beach you can go to any hotel out by Isle Verdi.The beaches are very clean .and easy to get on.One of the big hotels out there is El San Juan.By cab its about a 10 to 15 min.ride.Maybe cost you $10 each way.and there are cabs out there for your return.