Bottle feeding?

I am looking for articles that I can print to give to my daycare provider on why you should not prop a babies bottle up with a blanket or pillow. I walked in Friday to find my 2 month old in a bouncer with his bottle propped up and he was sucking air. The girl in the room wasn't busy with other kids so she should have or could have been holding my baby. I know it is not good to prop bottles for a few reasons, but when I complain to the director on Monday I want something to back me so I don't just seem like I am whinning. Any help would be great.