Nooks, Kindle Fire, and Credit Cards in schools!

Hi! We purchased a few nook color readers and Kindle Fires for our school to use in a pilot program.  With the nooks, it seems I am not even able to download a free app or book without a credit card.  This makes me very nervous, as they are a one click buy, and they will be in the hand of the kids.  How do you manage these tools in school?

We have apple devices, but they are password protected.  Thanks for any advice!