I have friends who have been. They enjoyed it during the day, but found the night times a bit of a waste because the kids needed to sleep and someone then had to stay in the cabin with them and missed out the evening stuff.

On just cruising in general, my mum is a cruiseaholic and her advice is to go with the best cruise company you can afford. P&O are really only 3 star (in her opinion) and companies like Royal Carribean and Holland America are much higher quality (food, accommodation, entertainment). I hear Carnival are family friendly but not sure about their quality.