According to the Skin Cancer Foundation, getting one blistering sunburn when you're a kid doubles your chances of developing melanoma.
Regardless of age and skin type (whether or not you burn easily), the American Academy of Dermatology recommends that everyone, adults and kids alike, apply a water-resistant sunscreen that protects against both UVA and UVB rays every day of the year. Yes, even in winter and on cloudy days. Choose a sunscreen that is at least SPF 30 and apply it 15 to 30 minutes before going outside.
When using sunscreen, apply as much as would fill a shot glass -- and if you're using both sunscreen and insect repellent, apply sunscreen first and then repellent.