Royal Caribbean has excellent children;s programs and I am sure the kids will have a very fun time. You do not mention their ages but I think you hsould go to the Royal Caribbean site and look u p the ship, and then look at "children;s programs"
Of course, for kids a lot depends on how many other kids the same age (or similar) are on the curise, but there are plenty of kids on most Royal Caribbean cruises.
I assume you have never cruised before? Almost any mainstream cruise line like Royal caribbean (Carnival, NCL) is going to have plenty of things for kids to do. If you are wondering about ships that do NOT cater to kids, look at the luxury lines like Regent, Silversea, Seabourn or Oceania.