Whatever you get, be sure that it's Coast Guard approved. Their approval indicates that the device will keep your head up out of water, and ensure that if you are unconscious you will float face up, not face down.

I've never seen a belt type device that will ensure you float face up. I've seen many people strap their kids into a belt with a float on the back. Well intended I'm sure, but very risky if they get a mouth full of water, start to panic, etc, etc.

If your kids aren't strong swimmers, err on the side of safety above all else. If you don't want to buy the vests, you can probably find a shop that will rent them.

I am also going down with your two children, ages 8 and 10. They are solid swimmers but since I anticipate being in the water for long periods I wanted to make sure they were as safe as possible. I purchased 2 snorkel vests for about $60 total via the web. I considered not getting them but once the idea was in my head all I could think about was what if there was a problem and they got hurt because I didn't want to spend a fee bucks for the right equipment.
I would not recommend a swim belt. They will tend to push thier butts in the air and thier faces into the water. My guys have used regular life vests snorkeling. These keep them above water and they can easily rest when needed but does not allow them to dive underwater to investigate.
Hope this helps. Have a great trip.

you can rent vests here at any place that rents snorkel gear. They are inflatable vests so you can have them deflated to snorkel and dive below, then blow them up when you need them. Also they are BRIGHT flourescent greenish so you can easily spot them if they stray too far.

You want a life vest that will allow you to have your face in the water, thus the whole point of snorkeling.

Can anyone suggest a place to rent snorkel gear at St. Thomas? will be there for a week.

www.sawyerdive.vi

http://www.aadivers.com/rental_rates.htm