Some players are having difficulty signing in to their Microsoft account on Amazon devices when using Amazon Kids (formerly Freetime). The following may help you resolve the issue:
- Go to Settings from the Child's profile (From the Child's profile, swipe down from the top of the screen and click on the gear icon) and then enter your PIN
- Go to Manage Storage > Internal Storage > Apps & Games
- Select the Minecraft app from the list and go to Permissions
- Switch toggle "On" and give permission for Storage
For more information about the tracked bug, please visit our bug tracker at MCPE-106524. Also, you can find some more detailed steps with images at the Microsoft help forum.