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Perhaps this helps:
/t5/Xperia-8482-Z4-Tablet/Apps-From-Unknown-Sources-Problem/m-p/1026050#M687
I want to know is whether a game installed on the main account, I give permission for my child's account so you can play. I find the way that the game is pre-installed on this account yet.
you will have to "re-download" the app from the other account, it will take less than a second as the app/game it's already on the main account.