RCI has childrens programs available on all their ships. I can say from experience, the Epic is a fabulous ship. There is so much to do, they even have a rock wall and 3 water slides. I know Sonny has sailed on the Granduer and I think Dave and Cruise Fanatic have, too. I can also tell you, the Epic is the same size as the Oasis and Allure, just a little more narrow, I believe they said 6" or it might have been 6', can't remember.
Cruise lines are really trying to cater to families. But from experience, the largest percentage of children/families I've found have been on Costa. I really love that line, too! RCI does a great job with children, though.