This card at the top of “Home” in the parent app is about YOUR phone, not the child's: your app hasn't contacted the server for several days, so while it was closed it couldn't tell you anything. How the child's phone is doing is written on its card below. Most often your phone stopped the app itself (for example, it was swiped away from recents). Tap “Allow background work” and choose “Unrestricted”; on Xiaomi also turn on “Autostart”.
“This app hasn't been online”
Protection off, a silent phone, no notifications. For the adult and the child