Purchases transfer to my child - already troubleshot with Microsoft

When I make marketplace purchases on my account, they transfer to my son. I have attached the troubleshooting transcript with MS. It has all the detail.

They are saying "this should not happen" and contact mojang.

 

I have submitted several relevant help tickets under my gamer tag Fellswift6660. 

 

We are honing in on the issue - I now know purchases are transfring to my son somehow.