We just ordered Blue Lizard after the reviews I saw for it online. Haven't used it yet, but it has zinc oxide (which is a barrier, not chemical protection), so I am expecting it to work well.
I also have my kids apply one of those face sticks to their noses, ears, chin, cheeks, forehead, etc... and reapply that often. It goes on a little bit like chapstick, which means that you have a lot of control putting it on. But if your kids use goggles or masks in the pool, you'll need to reapply frequently, b/c the friction of putting on/taking off the mask/goggles will rub it off.
Also, if your child is really that fair, (mine are blonde hair, blue eyed, so I know a little about being "fair") then you should not rely soley on sunscreen in a bottle, but get him into a rashguard Tshirt. My daughter loves wearing those and it really helps.
The areas that get the most 90 degree sun, is where you need to concentrate. If they swim and bob in the water alot-- then the scalp, tops of the shoulders, and face will get a lot of both direct sun AND reflected rays from the water. If they float on tubes or something, then the tops of their thighs and their backs need to be considered also.
We always apply lotion/creme about 30 minutes before going out, and then once they are in the sun/water... reapply with a spray (easier to do) frequently. But that initial application is with a creme. I have found that BullFrog works really well to block the sun... but it is laden with chemicals and not on any of the recommended lists for that reason.
For myself, when I run (shoulders take a direct hit), I apply Face Potion to my shoulders and arms (it is a barrier block, zinc oxide). It works well, but does rub off with any sort of friction... so you have to look at what your kid is actually doing. If they are in/out of the pool and wrapping up in a towel each time, then they are rubbing off the sunscreen with the towel and it MUST be reapplied EVERY TIME.
Good luck.
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After your SWH, I have to ask... have you asked his doctor? Could he have a sun allergy? I am not being facetious... but barring something unusual going on, I can't figure out how a child in a swimshirt and multiple applications of sunblock (4 x in 2hours? which means every 30 minutes right... and this is WITH a rash guard Tshirt?)... is still "fried". There must be something more to it.
Are you using waterproof sunblock? How old is he? And what time of day are you going out? 11:30 - 1:30 (the absolute most dangerous times of day)? Nobody gets a sunburn through a rashguard in 2 hours.... That's bizarre.
Does he take any medications? Some medications make people more sensitive to sunlight also. Or could he be having a photo-sensitive reaction to the sunblock you are using?