I just saw that Amazon is rebranding its Kindle Freetime Unlimited subscription (thank goodness because it was very confusing with Kindle Unlimited. It will now be Amazon Kids+ and they have an offer on till Oct 12 for a 3-month family plan for $0.99. My kids have enjoyed having a subscription. It is like having a virtual library on hand. It does not have all the new, best seller type books but it has a lot on there. DD7 loves reading National Geographic Kids books at the moment, and both kids have liked finding recipe books, art/sketching instructional books, and books to learn foreign languages. There are many good fiction books on there too. It is all curated kid-friendly content.

https://www.amazon.com/ftu/home