Late to thread but wanted to share my experience with taking a baby under 2 once.
I would never consider bringing children under 2 without a nanny and after my own experience with taking a nanny along one cruise-- would never do it again. I continued to cruise while having children under 2, however, but paid a nanny to keep my babies at home most often flying my mother in to stay with her for added security.
That cruise was hands down my worst cruise to date (out of 25 total).
My 'then' baby (now 14) became very ill and doctor visit on board $150 a pop had no clue what was wrong (turns out was infantile roseola-infant measles), put him on amoxicillin, (waste as viral illness), nanny became severely seasick almost immediately upon departure- her first cruise- and so I became 'nanny' to baby and 'caregiver' for the sick nanny all week, yet she seemed well enough to get up for dinner each night to dine in the main dining room while I hung back to care for my sick child... ???
Anyway, my experience is that programs for children don't start until 2 and so you're stuck with 'baby on hip' all week and it limits your activities a great deal. Other than that one cruise with the nanny I've never taken a child under 2, but I can tell you that I have witnessed couples with babies under 2 embarking the ship so happy and excited who weren't even on speaking terms by the time they disembarked. This one couple had no idea that the children’s programs didn’t start until 2 and they would not budge on their rules.
IMO, it is not worth bringing babies under 2 if you can't get a break from time-to-time, i.e., children programs that you know will accept babies under 2 or taking a nanny along-- and hopefully no one will experience what I did on my cruise from hell family vacation...lol