Hello TIO,
Welcome to Microsoft Q&A forum.
Before we proceed, may I ask about the clarification whether your son need approval to download or install a game? If the permission is for downloading, it will be delivered to your email, and you don't have to sign in to your son account to approve it. If the approval is for installation, you can try to use your Microsoft credentials to approve, if your son profile is a standard user, he cannot change the password or PIN of your profile.
I'm waiting for your reply.