At our house we don't really need sunscreen. We have these big cottonwood trees that provide shade over a lot of the yard. So, the kids are in and out of the sun when they are playing outside. This seems to prevent them from getting burned but also allows for their bodies to get the much needed Vitamin D that the sun provides.
When we are elsewhere, I try to pay attention to whether there is shade provided and how much sun their bodies are getting. This allows them to play without having to apply sunscreen but helps me be confident that they will not get burned. I will sometime have them wear floppy hats and clothes that cover their shoulders. This protects the areas the sun tends to hit the hardest.
I believe that sunscreen is used too often by most people. We were at the park the other day on one of the first nice days of the year, and I heard a mom yelling at her son, probably around 8 yo, to come and get sunblock on. I knew he would have to be outside for an extended period of time for him to get burnt in such weak sun, but apparently this mom was afraid of the sun. I question how often kids today are allowed to play in the sun without sunscreen on. Are they being allowed to get the Vitamin D that their bodies need and that tends to be lacking during the winter?