Good points about needing to recover two people instead of just one. We're on Lake Champlain and although we can get 4+ foot waves, we certainly would not be out in the wind that it would take to create those conditions. Even with 15-20 kts of breeze, often we're only seeing waves 1-2 feet because we'll hug protected shorelines. That said, wave action is one reason why my wife wants to go over if the kid does, since we're worried that a combination of going under in the fall, then panicking, then being tossed about in the waves might cause him to take in some water. So at least wife could help calm him and make sure he's not taking waves in the face. By 5-6 years old, maybe not an issue, but at 3 he has no concept of remaining calm in a stressful situation.
I like paperbird's reference to a quickstop within 1-2 boat lengths of the person overboard--that's impressive and I will definitely try this out myself to see if I can achieve similar results. I guess the main point is to practice and see what happens and what works.
Finally, the goal is obviously to not have anyone go overboard ever. But it's never a moot point because it can happen no matter the precautions so it's worthwhile to think about it and plan. I know some people tether, and that's about as much protection as you can get from going over, but really our kid would not like being tethered at all and I do want sailing to be a positive, fun experience. Under certain conditions I can see why you might tether, but for the type of sailing we're typically doing on the lake I think it would be overkill.
Thanks for all the tips/advice, etc!
If you want a real education on the subject, discuss it with your wife and have her agree to chuck a seat cushion (that you can afford to loose) overboard, unannounced, at some point. Ideally she should do so somewhat after you've had the discussion so it's really a surprise to you--and not something you're anticipating--and then sit down and keep still/quiet. It will take you a quite a few seconds--at best--to realize what's happened during which, even at a stately 4 knots, you'll cover several hundred feet. A child's head in the water, even with him/her wearing a "floatie" is only about 6" in diameter and I'll wager 10 bucks you'll have a hard time spotting it, even in small swells, to say nothing of 4' seas, just as you will the cushion. The quick stop maneuver will bring the yacht to a stop--but you'll have to take your eyes off the COB and if you do so, even momentarily, you'll likely not be able to reacquire the COB if there's any seaway at all.
I appreciate your interest in making sailing a "a positive, fun experience" for your child but relinquishing authority/common sense to be your child's "pal" is a fool's errand. Would you allow the child to travel in your car without wearing a seat-belt, even if you're only going a mile to the local convenience store? (I certainly hope not!) The same applies to the yacht. Ensuring the child's safety is your primary obligation as a parent, not ensuring that he/she has fun.
Our daughter sailed with use from the time she was a tiny baby. When she came on deck, she wore a PFD and a tether. No questions asked, no discussion. Her mother too wore--and still wears--an inflatable PFD on deck and puts it on just as she does a seat belt--before we leave the slip or "driveway".
On our boat we have a routine. When we're getting ready to leave the slip, we recite the "Rules". The first rule is "Safety First". The second rule is "Always hold onto the boat", etc. My daughter learned the Rules and could recite them by the time she was 2-1/2 years old. She's 19 now and still recites the Rules as do we all. Ignoring common sense safety measures for the sake of your opinion of "fun" for your child is overkill, and could very well end up being exactly that.