Standard Disclaimer: There are links to non-Microsoft websites. If you will wait to choose if I solved your problem, I will keep working with you until it's resolved. Feel free to ask back any questions and keep me posted. There is a thread here on Troubleshooting Family Safety here attended by a Family Safety rep.
Then sign into Windows 10 with that new account at Settings > Accounts > Family & Other People > Other Users (not Family, where it as originally signed up). Then you can change back to your MS account after/if it gets sorted out, or create a new online MS account to change it to. If that's not enough then I'd remove Family Safety from the child's PC by changing the child's account to a Local Account in Settings > Accounts > Your Info > Sign in with a Local Account Instead. However to get access to the child's PC you may need to remove the account from Familiy Safety settings in the Adult account and leave it disabled for the time being. What works most to fix Family Safety issues is to remove the child from the Settings on the Parent account, sign out of Family Safety, restart PC, sign back in to add the child back. If you will work with me I will be here to help until the issue is resolved.
I'm Greg, an installation specialist, 10 year Windows MVP, and Volunteer Moderator.
