I had my little guy (21 months at the time) riding in front of me on the jockey seat on the Searider last month. Taking a pretty calm, flat, fast trip across the bay. All of a sudden he pitches face down onto the steering wheel, and I realize that he's fast asleep! I stopped, laid him down on the deck and continued on my way.
He commonly sleeps in a stroller strapped down in the bow, for 3-4 hours while out coaching sailboat racing... The 7 1/2 year old will lie down on the deck for a nap as well.