Have you heard of Kindle FreeTime?
It’s a monthly subscription service on the Kindle that lets kids choose from thousands of the most popular books, games, apps, and shows. There are no ads and no in-app purchases, so you can rest assured that your kids aren’t going to accidentally purchase something. You can set up to four different profiles for your kids and you’re able to limit their time … and limit it based on category (limit videos and set unlimited time for reading).
Right now, you can sign up for a free trial of Kindle FreeTime. After, you can subscribe for $2.99 a month with Amazon Prime and $4.99 without.