If these are '12" volt panels with a 12 volt battery
system? Id disconnect the charge controller and separate the panels. Then check battery
voltage, make sure they are not at 100% charge, discharge them if need be. Guessing to the 60-80% charge depth
Now take each panel, one at a time. Connect directly to the battery with an ammeter in line, and see what the panel is putting out. Check again to see what voltage is it putting out, under load to the battery. (Faster if you have two meters.)
If each panel tests OK by itself, as I suspect they will, then the charge controller is the problem. If the batteries overcharged and that controller is their only charging
source--that's a finger pointing to the controller as well.
I suppose it is possible, depending on what was connected and how, that a diode failed, the panels took too much reverse current
, and some cells burned out ruining all of them. But that kinda seems way less likely.
Divide and conquer, get the charge controller physically OUT of the picture and see how the other kids
play without it.