There's got to be a better way
I'm not sure where you're sailing, but I sail with 3 kids, including a 4-year old, and they absolutely love it. Sinking is not very likely, but a MOB situation with a 3-year old is.We enforce our rules for them, and we feel very safe.We don't allow them on deck without a life jacket, and I have a harness for them (that I've never used) but could use if I ever got worried enough.I'll bet it would be a lot easier to buy some safety gear than to deal with towing a dingy the size of your whaler.Depending on how you tow it, it has the potential to give you and your boat a beating exiting and entering your slip, at anchor, etc.Get your kid a good life jacket, a harness, some glow sticks for nighttime, and one of those flashing strobes. Add some lifeline netting to the boat, too, if you need to.The probability of your boat sinking in conditions you would feel safe with a 3-year old in are pretty low.Some of the best boating video I have is of us heeling at 20+ degrees outside of Mobile Bay and trying to hold on in the cockpit, but then the camera shows inside the boat and you see my (then 3 year old) asleep on the rear berth. To us it's a small boat, but to him it's huge.Good luck.- Stan