The following is on an Amazon Kindle Fire 7

I think I have spotted a bug regarding Minecraft Coin purchasing (and add-on purchasing) through an Amazon Kindle Fire.

To reproduce:
1. Set a child's profile to "Enable in-app purchases"
2. Using the child's profile buy Minecraft coins through the Minecreaft app
3. Use Minecraft coins to buy an add on.
4. Start using the add on
5. Change the child's profile to disable in-app purchases
6. Using the child's profile start playing Minecreaft again
7. All Minecraft coins have gone and the add-on is disabled

I have contacted Amazon who believe the issue is at your end.