I found this website and found it to be incredibly useful in understanding about sunscreens. It is a huge read for busy moms but well worth it when you consider that it does not recommend some of the most popular brands of sunscreens like Coppertone.
It breaks down each product by toxicity and by effectiveness. It is interesting that it also recommends a common drugstore brand above the leading ones in the field.
This site is not limited to sunscreen but covers all manner of cosmetics and skin care. I also like the fact that this is primarily a research group, not affiliated with any company and not trying to sell any other product of its own.