With multiple generations as you describe look hard at Princess and Royal Caribbean. Princess has more ships/itin's to offer. Another good choice is NCL's new Pearl. I've recieved extremely good reviews from clients on her.
As Cruise Fanatic points out Holland also has a major presence there, like Princess. However with small children I'm not sure that would be the best choice.
Whatever you decide have a great time and let us know how your trip was when you get back.