I do require the natural stuff. I had a mom who didn't comply, so I just used someone else's on her daughter.If you're really worried about it, I'd verbally talk to parents about it.."oh know what, today at nap time, I was reading about sunscreens, and I was appalled at the crap that goes into them. I am throwing out all of mine, and getting the natural kind...it penetrates the skin and goes into my kids' system, blah blah" See what they say. They may ask you to suggest a brand.
ETA: I kinda live in a hippie type neighbourhood, so it wasn't a hard sell.