Children are very interested in doing things with friends, less so with younger siblings. At some point, after the initial novelty wears off, you might be farther ahead to send a couple of them off on land with some friends, while you take the others and *their* friends sailing. This works well if you are friends with a family who have some similarly-aged kids. My guess is that the 14 year-old whines moderately about the 12 year-old, and the 12 year-old whines a little about the 6 year-old, and the 6 year-old whines endlessly about the toddler.
My six year-old son didn't care much for being on deck, but he loved loved loved being below and playing with the dishes in the galley. It was like a kid's kitchen. And keeping him below made his mother and grandmothers less frantic, though I think it was probably *less* safe in fact. Head injuries are forever.