My parents own a boat, and keep a Stearnes life vest for the little children that come aboard. This vest has a cute Tweety bird on the front, and fit my two-year old really well.
This vest has three adjustable nylon straps that you can tighten around your toddler without it becoming uncomfortable. My daughter went into the lake swimming wearing this and it is very bouyant. She did not complain about having it on so I assume it was comfortable. Through several seasons of heavy use, the buckles are still in place and there is no wear on the nylon fabric.
I have had experience with this company and their infant vests. The vest they make for small children and toddlers seems to be of the same great quality, and I would highly recommend owning one if you find yourself on a boat with your kids.