We keep our PFD's in the cockpit area within reaching distance when we're underway. Yes, there's always a chance that one of us (or all of us) go over without a PFD, but that's always a risk. If it was blowing good, and/or if we had cold water (it's in the 70s right now), I'd have no qualms about wearing my PFD.
I actually like the plan of my wife going in the water, but I insist that she first puts on a PFD. (Sort of like the oxygen mask on the airplane.) When we talked about it, she didn't want to take the time to put on a PFD, but I convinced her that the 30 seconds it takes to get the PFD on is worth it.
I wasn't sure if that was just a crazy idea to have another person go in (seems counter intuitive), but the thought of my 3 year old being alone in the water while I try to get back to him, puts a knot in my stomach. As long as my wife gets to him, I can take as much time as I need to get back around to them (which is why I'd consider starting the motor and dropping the sails).
What I do need to learn is how far back he would be by the time wife is suited up and in the water, assuming I had immediately rounded into the wind. I guess an easy way to test this is just throwing over a PFD some day and practice getting back to it.
We will also practice a "kid overboard" drill on a light wind day and make it fun. We swim off the boat at anchor
all the time, so the water itself and getting up the swim ladder
is very familiar for all of us. Just need to add the variables of being caught off guard and a moving boat.
ETA: Oh yea, kid has the PFD on at all times. That's a given. He's allowed to take it off below, but unless he's down there sleeping, he usually still has it on.