Do your kids wear sunshirts? You may want to consider that to protect their backs, shoulders, necks. You can buy them at walmart or target (they have special UV coating built into the fabric).
Don't forget hats too!
One thing I hate about all this sunscreen .... is I come back from holidays, and no one can tell I've been away! I'm naturally dark, so i tan easily, so do my kids. We went away in March, and not one person could tell that we had been south for a week.