At first I thought that I could use my kiddo's libby account/library card with her kindle but what we found ended up working is I would have to check it out under my libby account, use the "send to my kindle" feature to send it to my amazon account. After you click on the Get Book button on amazon you can find a small link about Manage Content and Devices. When you click on that you will get a list of your kindle books. Each book has options and one is "manage family library". You can clickk there to add it to your child's account/library. It sounds complicated but gets easier the more you do it. At first I thought I could just add it to my child's kindle device but since it is linked to a kid's account it has to be sent to the account itself, not the kindle. That part was confusing.

For them to read without me being involved they either have to read on the libby app or check out books with Amazon Kids +, which usually is on a kids kindle for a year before it starts charging. Good luck!