1. Open the Kids+ App.
2. Press the Cog wheel to reach the settings of the account for which you want to enable In-App Purchases.
3. In the Manage your Child’s Content section, you will find the option to Enable In-App Purchasing. Move the toggle to the “ON” position. (You will have to repeat this step for every child profile linked to your parental profile.)
4. Exit the settings and press on your child’s account to launch Kids+.
5. Launch the app from the child’s Kids+ account and make your purchase.
6. Type in the parental account password to confirm your purchase.
7. Your Purchase should immediately unlock once processed.
  

Please Note: Even with this setting enabled, your child will still need the Amazon account’s password in order to make in-app purchases. Note that In-App Purchases are only available in the account in which they were made.