Now how did I miss this thread all summer?
We daysailed with our kids of 2, 4 and 6 all summer and had a total blast. Had tons of their friends on the boat for short sails and they mostly liked it (one 3-year-old wouldn't keep his pfd on, one 6 year old found the whole thing scary). All the kids were totally up for a long day at the beach and on and off the boat. Sails were not more than an hour or two punctuated with lunch and snacks.
Cabin time was a bust mostly, but our cabin is pretty unappealing. Anchoring out to swim is unlimited entertainment. The 4 and 6 year olds liked taking the helm (my 6 year old daughter knows far more about sailing than her mother, she's always on hand to grab the helm so I can go forward or trim sails). Driving is most fun when motoring when the kids can go any direction they want (with lots of lake room and no other boats around, and daddy keeping careful watch). All are still too scared to jump off either the boat or the pier but it'll come. The two year old loved watching the other boats go by and easily fell asleep in mommy's lap, we need to make a cozy nest for him in the cabin. Motoring or sailing, it puts him out quick