The best time to put on sunscreen: 20 to 30 minutes before your child heads outside. That's how long it takes the chemicals in most sunscreens to work. Get in the before-you-walk-out-of-the-house habit even if you're using an effective-at-once formula like Banana Boat's Surf or a physical block with zinc or titanium oxide. That way, your little sun lover will be protected while you fiddle with the beach umbrella. To find a good sunscreen, look for the Skin Cancer Foundation's seal of approval (which means it provides UVA and UVB protection). And reapply every two hours.