While the child is in my care, it is my responsibility to keep them safe. If the child gets burned in my care, I am the one to blame. I would explain that we as a group go outside, and sun protection is required in my program. Maybe suggest SPF clothes and a wide brimmed sunhat to decrease the amount on sunscreen needed. All exposed skin will still need adequate sunscreen applied. A thin layer will result in not getting the full SPF level listed on the bottle.