I've been told that the best PFD you can buy for kids as far as safety and comfort go is the "Mustang" brand that
@GTBRMC attached a photo of. That said, if I had purchased those jackets they wouldn't have been needed because it would have eaten up all the boat-gas money considering how fast my 4 kids grow.
We've had several struggles over the years with Life-Jackets: My two older daughters have developed rashes from certain materials and/or colors so there have been years that we've had to buy multiple PFDs to keep everyone happy and comfortable. Suggestion: If you have multiple children (especially if you've got at least "one of each") then get neutral colors. Your son will not appreciate the hand-me-down of a pink life jacket that his older sister has outgrown.
As far as getting them to keep it on. Well, that's where your authority as a parent comes in. We have ways of making you wear your PFD. (Use a Russian or German accent for that one - your choice.) There is a problem, of course, if it's someone else's kid giving you trouble. If that happens then the trip ends and folks just don't get re-invited. Safety is not a subject open to debate or worrying about hard feelings.
WI requires PFDs "when underway." So if you're not anchored or tied to a pier/dock, then you're considered "underway." (Drifting is defined as "Underway with no way on.")
Our rule is that you WILL wear your PFD in the boat while underway. This applies to adults as well. As Master and Commander of this vessel, you will comply by my rules or enjoy the day from the shore. Your choice. I don't want the added worry of wondering how long you can swim after you do something dumb and fall overboard. I'd rather take my sweet time to come back and get you. (I have made only ONE exception to this rule: My Sister-In-Law's husband is an amateur body builder and finding a vest to fit him reasonably would be nearly impossible so I just had him sit right next to one of those cheap "horseshoe" type PFDs. He could have gotten it on if he HAD to in an emergency - we did make sure of that, but it wouldn't have been much fun.)
At anchor/at the dock is another story. When we anchor to swim, you may remove your PFD. If you are a child, you WILL wait until Mom and Dad are ready to have "eyes on" before you go out on the swim deck. At the dock, I make them keep the PFDs on until they are away from the water area. Chris and I keep ours on as well just in case something stupid happens during recovery.
(You'll notice I'm kind of a "d**k" when it comes to safety. I spend 8 hours a day in an industrial setting and I know what happens when you ignore or "look away" from safety rules. These may be toys we are playing with but they are big pieces of equipment operating in an environment that human beings do not normally operate in. We need to keep our focus on safety. And believe it or not, you can still have fun while being safe. In fact, you get to have more fun because bad situations generally don't go "from bad to worse" when you've got your safety controls in place. So you fix the bad situation and get on with the fun.)
The good news is that of the 4 kids we only have one left who cannot "truly" swim yet - but he's getting there. In fact, a few years ago, the eldest daughter pulled John from the pool after he "forgot he couldn't swim" (Boys... I swear...) and went in without water wings. (The adult present (their Uncle) was watching and was about to dive in fully clothed, but Katie had John out of the water before you could say "boo" so no phone or wallet got ruined.) I wouldn't rely on their swimming ability for safety, but it's nice to know it's there if things go really, really wrong.
Post-swimming can be an issue for the ones who still have to wear PFDs while swimming. Usually it means putting on a cold and wet PFD when it's time to get back underway. Once again, having older kids has helped this problem because now we just use water-wings on John. Matt actually has two PFDs with us - his own and a hand-me-down from John that he wears while swimming. This keeps the regular PFDs dry.
One thing about toddlers on the beach and in shallow water: Do NOT put life-jackets on them. They tend to fall over forward and cannot "get their feet under themselves" to stand back up again. This leaves them face-down in the water. We learned this quickly with our Oldest. Of course I was standing within 6 inches of her and staring at her the whole time so we only got a minor scare. Had I been relying on that PFD to keep her safe... well - who knows.
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