Locating IPhone in Find my

I have my family all linked in my ‘find my’ iPhone. A handful of times while checking my children whose phones are fully charged, the first couple seconds of opening the app and seeing their device, date and time are red as well as in a random location. So typically that means the phone was last there and the red means their phone is either off, or location turned off. Within maybe 30 seconds it quickly updates and shows their current location and green indicators.

The device was checked about an hour ish before this and was on and live. So my question is:

If I’m checking a devices location and it’s live, the next time I check it is randomly red but then updates back to live, does that mean the device was turned off at some point to trip the “last location” red? It’s not location being turned off because the parental settings. I want to see if my child is turning off their phone and turning back on to avoid me seeing their location. But wouldn’t the red indicator, especially if earlier it was not red mean the phone was turned off?

is there a way to see within iPhone or family when someone turns their phone on and off?

pics attached. First being as soon as I opened I quickly screenshot and then 30 seconds later is the second picture. What would cause that?