Well, the Legend is bigger than Inspiration but not super huge. (Inspiration is 70,000 tons w/2,050 passengers and Legend is 88,500 tons with 2,124 passengers.) Since I haven't been on it, I can't tell you how it'll be.
I'm surprised to hear there weren't that many activities b/c Carnival carries the most kids of any line at sea. We were just on the Carnival Triumph and my kids enjoyed the youth programming. But if you had a not great experience on Inspiration, you may want to check out the many big ships sailing from Miami or Ft. Lauderdale.
Let us know what you decide.
Family Cruise Editor