C.D.
We are going camping/boating in two weeks and had to buy our 10 month old a life jacket. We tried the ones that you described that split around the neck but she just screamed the entire time we had it on her at the store. We decided to go with one we found at Walmart, it fits like a swimsuit, with the flotation peices around the back and waist.
We figured since she is going to have to wear this for an extended period of time, comfort should be a high priority as well as safety. They also had boy ones that fit like a short suit.