Hi @mehdi , Welcome in Community
If your son's Windows 11 PC is not appearing in Microsoft Family Safety, the issue is usually related to how his Microsoft account is configured on the device.
First, make sure that your son's Microsoft account is correctly added to your Microsoft family and that the account is being used to sign in to Windows 11. On the PC, go to Settings > Accounts and verify that his account is correctly connected
It is also important to check that your son's Windows account is a Standard user and not an Administrator. Family Safety may not work correctly when the child's account has administrator privileges
After checking this, sign your son out of Windows, restart the PC, and have him sign in again with his Microsoft account. Then check the Family Safety dashboard to see whether the device appears
If the PC is still not detected, check whether Windows shows any Verify prompt for his Microsoft account under Settings > Accounts, and complete the verification if required
Let me know how it goes
Elvis