I just took my two year old daughter swimming last saturday and I kept reappying her sunblock so she did not burn but I got second degree burns they claim to use cool baths, aloe, and things like that but I had to get the dr to perscribe a cream called silvedene (I think thats how it is spelled) because my burns are that bad if hes blistered I would take him to the dr.
It is best to try to keep hats and long sleeves on when possible. If you use sunblock, you need to make sure that you wash it off of them as soon as you get home because it is purely chemicals that their bodies are soaking in.....just something most people don't think about. The treat a sunburn you need vitamin E oil. It gives the skin nutrients and balances out the damage the sun did to the skin. Giving the skin nutrients allows it is begin healing. I would just apply a pure vitamin E oil. I find it in the vitamin section, they come in small bottles.
you can put some vinegar/water on a soft cloth and pat it on her burns.... it's smelly, but the vinegar will take the sting out of her burns and soothe her. it's what my mom used to do for us when we were kids, and what i do for my girls too. it works great!
My aunt passed along this remedy for sunburns and it works great. In a large pot, boil water and steep about 10-20 tea bags for at least 10 minutes. Once tea is ready, add ice until it is really cold. Soak wash cloth in cold tea and apply to burned areas until washcloth gets warm. Continue doing this for 10 - 15 minutes a few times a day. I have burned myself numerous times living in southern california and I thought for sure I would bubble, since I have many times in the past but this helped and I did not bubble.