We have two boys, now 11 and 9, adopted last year. I only mention that because they had zero - and I mean zero - water and boating experience before we got them. Couldn't swim one stroke, would sink to the bottom like a rock. So we did swim classes, summer sailing camp, trips to the City pools. We spend every possible weekend on the boat with them, including overnights. Happily they swim and dive like fish now, never seasick. I have them run the dingy (9 foot Zodiac with a 4hp Yamaha). They help on the boat, although they have very little endurance for drudge work like scrubbing decks or cleaning. My 11 year old is skinny and he's very handy for engine work that I can see but not reach. I talked him through changing a fuel filter in a tight spot between the hull and engine last year. Nicholas helped me set a new snap on the canvas today. Lubed zippers. Powerwashed the carpets. Taught them the whole routine about boat toilets and they picked it up very easily. I explain the electrical panel to them as I go through it for opening and Ieaving the boat each weekend, although it'll be a while before they understand the whole panel. In other words, we involve them in every possible water and boat activity including maintenance. In our experience so far, you involve kids in boats and water life and I'll bet it's a rare kid who won't take to it and love it. Kids are incredibly adaptable.
Photo of Matthew at the tiller of a Hobie, his second day under sail of any kind.