Q: refund a purchase

All sales are final. Not liking the book that you read is not a reason for a refund.

My five-year-old grandson purchased Minecraft and I did not know this and I was just charged $6.99 on my credit card how do I get this removed

It's not a book it's a game it's called Minecraft pocket addition

As the above reply says, purchases are considered final but you can try the 'report a problem' page to contact iTunes Support and see if they will refund or credit you : http://reportaproblem.apple.com

Or you can try contacting iTunes Support via this page : https://support.apple.com/contact or

https://www.apple.com/emea/support/itunes/contact.html

If you haven'y already done so change the account's password if he knows it, and if the purchase was done on an iOS device use Settings > General > Restrictions on it to try and stop it happening again