Hello Sarah-Jayne Turner,
Welcome to Microsoft Q&A forum.
Before we proceed, may I have a photo of the situation to check for you? Please remember to remove all personal information before posting.
In the meantime, please try this quick fix.
- Type "Credentials Manager" in the search bar and press Enter.
- Go to "Windows Credentials"
- Remove all entries
- Contains "Xbl"
- Contains "Mojang"
- Related to your son's account.
- Restart the PC.
If the answer is helpful, please click "Yes". If you have extra questions about this answer, please click "Comment".
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