This year my two year old wore a puddle jumper. I found it in Walmart for $10 but One Step Ahead was also selling them. It is like swimmies but also goes around the chest and instead of being inflatable it is like foam/lifevest material. It is coast guard approved. It was tight enough that my son could not get out of it on his own but his arms would come out if he wasn't swimming in the water, mainly when he got out or was playing on the steps. I would never ever leave him by himself in the pool but we were able to swim all around w/out me holding him at all. He loved it!
