We cruised the Keys with my daughter when she was barely a year old and it was alot of fun. She wore a life jacket most of the time and if we were underway, she was tethered to a cleat. Belowdecks; lots of pillows around and we secured her between us at night in the v-berth. During the day, she took a nap her in a car seat. Like most parents, I was a little apprehensive, but cruising with a baby onboard was relatively easy.
One of the best nights was when my parents motored out in their cabin cruiser, tied up along side for the night and helped out, kinda like nautical babysitters. That was a few years ago, as my daughter is now nineteen.