This article explains how to put an Amazon tablet into Kids Mode. The instructions apply to all Amazon Fire tablet models.
How to Set Up a Fire Tablet for Kids | Amazon News
Before you can switch to this mode, you must set up a child profile using the Amazon Kids app. You can have up to four child profiles per device. If you have already created a child profile on your account, you can use the Amazon Kids app to customize what content your child can access.
Open the Amazon Kids app. If you don’t see it on your home screen, download it from the Amazon Appstore.
Tap Use Amazon Kids with your own content. You can also choose to sign up for Amazon Kids+. An Amazon Kids+ account is not required to create a child profile.