This is the generous interpretation and the one I’m picking. Seems like a stressful situation for all, so a lot can be forgiven.

I can even understand “k” as response. What can mum do except give the kid, and mum, space to solve the problem? “I understand, I’m calling the police now” or just call the police. One saves time, one wastes it.

I could even understand it being a “oh shit, oh shit, oh shit” response. Executive function is gone, here’s a “k” while I melt.

Lots of room here before jumping to mum being the worst person in the world.