After I found out that thermal receipts contain BPA, I stopped letting my son play with them. He used to love grabbing them from me and holding onto them (sometimes chewing on them). But now I don't let him. I also try to wash my hands after touching receipts (not always easy!). I don't know exactly how toxic they are, but I try to avoid them just in case.

http://www.ewg.org/new-study-confirms-BPA-exposures-from-receipts