Parental controls screen time limit being used up by system settings or idle apps

I have put on the screen time limits for my children however, they are getting a time up notice at the beginning of the day because they have used up, so to speak, their time due to system settings, passwords or other idle apps running in the background. When I look at App and Website Activity, I indeed see that they have been "active" for many hours with idle apps including system settings running in the background or at night, far exceeding the App Limits. At the same time, the downtime is not coming on at the designated time and they can basically continue to use the computer as they wish. I have done everything necessary - updating, resynching, ensuring block at downtime, scheduled, app limits, turning content restrictions on and off, and nothing helps. They are family members on ICloud. Can someone help?