The best kids vest I have seen are by Stohlquist and Astral. Both are made for 50-90lbs, which should be perfect once summer rolls around. These are "real" PFD's.
We (Down River Equipment) are a dealer for both companies, but they are not jackets that we have ever stocked. If you can not find them via the web, give me a call and I can make an order. Since it is not a stocking item, you wouldn't be able to return it if it didn't work out.