TBH, it is hard to make any recommendations without knowing a little bit more. How old will the child be? How long do you want to go for? Where are you thinking of going? Are you the kind of family where you like to use the Kids Clubs? Most of the onboard children's programs are for ages three and up, and parents can't join their child, it's a drop off and return type situation - floating daycare! Each line has its own selling points for families - for example, Carnival (who will soon start departures out of Melbourne) has the Seuss at Sea program, and that includes character meet and greet opportunities, as well as a character meal. Most lines have something along those lines, but it depends on what your family likes to do on vacation.