I bought one for each of my three very, very fair (OK, let's just call them see-through) kids. They spend a ridiculous amount of time in the water, at ocean beaches, lakes, water-parks and pools and sunblock just cannot keep up. These hats are great! They will still get a bit of sun from the water's reflection, but the hats block 100% of the overhead light. My three do swim underwater with them and they usually stay put, (goggles over the hat flap works even better). When they really get whitewashed by a wave or dive in the water in a wacky way the hat can come off, but - it has a FOAM VISOR!! It floats!!! Love these for everything they do outside. Bonus - I can find them in a crowd (like at swim lessons) so easily - they each have their own color. If they were a bit less $$ and had a larger range of sizes I would have rated 5 stars. (For example; I used the size chart that gives inches instead of ages - found it on Google - and they fit my kids just fine, but I can't imagine it would have worked so well for a kid who is in-between . . . too much give and it won't stay on, too little and I imagine it could get uncomfortable). Here's the chart I found with head measurements (I don't understand why Swim Outlet doesn't have this??): XS=15-17 inches   S=18-19 inches  M=20-21 inches    L=22-23 inches  If I had an in-between kid I would  just order the size up - they'll grow into it!