Hi CS257,
Thank you for using the Apple Support Communities! We understand you're experiencing an issue when using parental controls on your child's device's. We'd like to help.
It sounds like you have Family sharing set up, and these child device's are part of your family. Please review this article to confirm how you have parental controls configured for those devices: Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support. What part of the parental controls is not working as expected? Or, are you saying the parental controls are completely being removed from the devices? Typically, that can only occur if your password becomes known to the users controlled under parental control, and they enter that password to disable restrictions. We would suggest setting up a new password for the parental controls and testing that possibility out.
Best regards.