Hi T.- isn't it amazing we're already getting to that time of year?
My sister is in Dermatology and she basically insists that we use Neutrogena UltraSheer SPF 55 with HELIOPLEX. It's lightweight, oil-free, PABA free, UVA/UVB protection, etc. We use this day to day.
We also have a boat and are very active in the summertime, sometimes going out several times a week. For water play, we use a product line called Blue Lizard. It's an Australian sunscreen that comes in many different formulations- regular, sensitive, face, baby. You can now find it at some drugstores or dermatology offices. This has the same protection as the Neutrogena, but it stays on much better. My sister says that Australian sunscreens have to pass much stricter guidelines than American sunscreens. These sunscreens are more expensive, but they're worth it for our family. Both of our kids have fair complexions, and even by the end of the summer, they have hardly any suntans.
You have to reapply ALL sunscreens, especially if the kids are sweating or swimming.
Good luck!
J.