I had never thought about this as an issue - and I have a child who is very sensitive to scents - the few I have made have had the sheets put through the dryer many times - use them until they are useless - then iron them between newspaper to get the oils out of them.
I am glad that I have only made a couple of them and will rethink using them in the future. I know that it might seem like a small thing to some people, but to others it may not.
Personally, I don't use dryer sheets anymore since my Maytag book says not to, evidently they aren't good for our dryers - who would have thought ...