that's a hard one, Ted. I struggle with that question often. I tend to just look for another market.
I think I error on the side of being overly cautious.
But, I also know that that sort of a statement has to be made because otherwise? (especially in the horror genre) the slush pile ends up full of a LOT of stuff that is not well written stories, but platforms for people to write hateful things, pornography, and more.
I think, if it's a horror mag, they are expecting unsettling things. And as long as the harm to the children happens off screen, or even better is only implied, you might be ok to sub anyway.
Even still, I tend to look to the mags that say they take anything, no subjects off limits.
Have someone(s) read it and let them weigh in on how strongly it comes across.
I don't know if any of that is helpful.