For Family Safety, the child’s device must be connected through the child’s Microsoft account on that Windows PC. The supported path is not to convert the parent’s local admin sign-in to a Microsoft account.
Use this setup on the child’s PC:
- Sign in on the PC with the child’s profile.
- Open Start > Settings > Accounts.
- Check whether the child is signing in with a Microsoft account.
- If not, select Sign in with a Microsoft account instead and use the child’s Microsoft account.
- If an email address is already shown, that is the account that should be in the family group.
- On the parent/admin side of that PC, go to Settings > Accounts > Family & other people.
- Under Your family, select the child and then select Allow.
- Make sure the child account is a Standard user, not Administrator.
- Have the child sign in. After that, the device should appear in the child’s connected devices.
If Family Safety still does not recognize the device:
- Re-check that the child is still listed under Settings > Accounts > Family / Family & other users.
- In the child profile, complete any Microsoft account verification prompt if shown.
- Sign out of the child profile, restart the PC, and sign back in with the child account.
- Allow time for sync. A registered device can take up to 24 hours to appear.
Important limits from Microsoft:
- Non-Surface Windows 11 devices are added automatically when signed in; they are not manually added by serial number.
- If the PC is managed by a company or organization, it cannot be registered to a personal account.
- Family features may not work properly if the child account is set as administrator.
The dialog shown is trying to switch that Windows sign-in to a Microsoft account on the current PC. That is separate from the documented Family Safety device-connection flow, which is based on the child account being added to the PC and signing in there.
References:
- How to connect a device to a Microsoft account
- Fix family features after Windows 10/11 upgrade
- Manage devices used with your Microsoft account
- Microsoft Family Safety not recognizing my child's device under his profile - Microsoft Q&A
- CHILD has an Administrator account that could break Family Safety features - Microsoft Q&A