I think that they really do try and target the activities for the specified age group. My DD was just shy of her 8th birthday on our 5/27 cruise, but she is tall for her age and in the 2nd grade. She was very happy to be in lab and loved making flubber, having computer time and playing games up on the sports deck. The club had things that I thought the younger kids really enjoyed, like playing dress up and magic shows. A little more in the way of entertainment for them.
I was really happy with the kids activities and I honestly had no idea about what my daughter would choose to do. At breakfast, she would look through her navigator and plan out the whole day. One night she ate 2 dinners, one with the club and one with us and on another night, she chose to have dinner with the club and then stay to make flubber.