I've been on Carnival and Disney so far - and soon will be going on Royal Caribbean. It's always been without children travelling with us. Now, most of my experience has been with Disney and the Carnival Cruise was the worst experience of any vacation I've ever taken (to the point that we said on the second day we'd rather have been at work) so that may influence some of my perception.
With regard to kids on the cruise though I found Disney did a MUCH better job of giving kids something to do so they simply weren't around a lot. Sure, in the family pool area they were there, splashing, running, squealing - just like they ought to! They're kids! But, in the adult areas, Disney did a really good job of ushering kids out (politely in the Disney Way) than Carnival did. I've heard similar things from friends who've been on other Cruise Lines.
So - true, there are more kids on a Disney Cruise - but they have so much to do, you notice them less if you choose to frequent adult areas of the ships.
