Greetings!
This is Tin, looks like you added your account and accidentally removed your parent's account on the device.
Please go to Settings, Accounts, and choose Family, under Family, please look if your parent's account is there. If none, since you've mentioned that it's on the lockscreen, there's a possibility that you logged out your parent's account and sign in your account instead. To set it back, please click Start menu and type Your Info then hit enter. Click Sign in with Local account instead then follow the prompt.
After that, please go back to Your Info page and choose Sign in your MS Account instead and ask your parents to sign back in.
Please let me know how it goes.
Thanks,
Tin