Ok, a bit of a yarn to set the scene.
Under Windows 8.1, on my child's tablet, logged on as them, I would change the Store login to my account, to purchase games and apps and install them.
Now this is no longer possible, the store can only be accessed using the currently logged on account. I have a decent investment in children's games under my account. Additionally I redeemed the free Minecraft offer, associating it with my account. Whoops. I'll use it as the example.
But all is not lost, I have figured out a way to get my child's apps and games to work under their account. I would just like to know why this process works, and if it's official.
My child's account is configured as part of the Microsoft family safety system, so their account is listed as a child of my account.
On a new Windows 10 install, my child's account is unable to install Minecraft, being prompted to pay $15 and add a payment method.
If I log into the box, and install Minecraft, my child is now able to click on the $15 purchase button, and it will install under their account, without prompting to purchase.
In fact this process then continues working for all the other games I previously purchased under my account, even without me installing them under my login first.
I have not been able to find any official statement about this, and I am left wondering due to the fact that there is no indication in the store that my child is entitled to install these apps and games, and it requires a leap of faith by clicking on the purchase button. Additionally, me logging in the machine is not enough, installing the first app seems to kick something off.
Perhaps @nathan knows?