So this is the top view of a Safariland 6360. As you can see, there's a large channel to allow the light to fit inside the holster. It's the area that ends in a circular cap on the right side of the holster from this perspective.
From this angle, you can see the gaps that exist on either side of the light. This is because the light is wider than the firearm itself (specifically the trigger guard), and the channel needs to be wide enough to allow the light and trigger guard to both fit.
Here my gun is fully seated inside the holster. Note the gaps are now around the trigger guard.
As you can see, I can pretty easily fit my pinky inside the trigger guard. You can't see the hammer in the photo, but I am able to pull the trigger with minimal effort. A child would be able to do so even more easily with smaller fingers, I'd imagine.
Now, here is the exact same model of holster, but without the light-bearing feature. Note that there is no extra room to accommodate a light.
Without the extra space for the light, the gaps around the trigger guard are almost non-existent.
There are two solutions to this problem. One is to blame the equipment for being faulty and prohibit it's use. The other is to blame the officer for not noticing that someone was finger-f***ing his holster, and stress the importance of maintaining better awareness, with disciplinary reaction resulting from a failure to maintain that needed awareness.