I originally wanted to get my daughter the Mustang life vest because it has the most flotation but she was in-between sizes so I got her the SeaFit and it seems to work just fine... This past summer was our second season with it. She's 2 1/2 yrs old now so 2 summers ago she was about the same age as yours.
When I'm rafted off I swim with her in the vest and it provides good flotation.. The mustang, if he fits, has a bit more flotation.