Like for any burn, the first thing to do with sunburn is put it under running cold water to pull out the heat of the burn.

I hate to admit that our daughter got sunburnt last week - she was sunscreened but her top rode up as she rode her bike and foudn the spot we had missed. Instead ofputting her in a cold shower, we stood her in the middle of a garden bed and hosed her back It helped her sunburn and watered some plants - so although we technically watered the garden out of restriction times, it was better than putting her in the shower.