Before my daughter's first summer vacation, I purchased a Stearnes life jacket for her so she could go boating with us. These life jackets are made especially for little ones.
They have a pillow that floats behind the baby's head when they are laying back in the water. I put my daughter in the water while she was wearing the life vest and she loved floating on her back. Her head never got in the water and she never rolled over.
There is a strap that goes between your baby's legs to keep the life jacket from slipping up over the baby's head.
Just from playing in the water with her wearing it, I got the sense that this is a high quality life jacket that would keep my baby safe in case something were to happen while out on the water.
The bulk of the jacket is rather constricting, and seemed a little uncomfortable to her when it was zipped up under her chin. That was the only drawback I experienced.