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#11
In order to get an activated Windows 10 again you are going to have to do a clean install of Windows 10 Home. Skip entering the product key if you are asked for one. Since you had Windows 10 Home activated on that computer before, it will activate again based either upon a product key stored in bios or by retrieving a digital entitlement from Microsoft activation servers.
Then set your son up with a user level account instead of administrator account and keep your own administrator password to yourself