She'll find that the three of them are gathered around a second-floor window - quite literally, as they are stuck to the wall around the window somehow, staring into it intently the way normal children might gather around a puddle containing a frog. They look up at each other, and the tallest one pulls something round of out their pocket. It's hard to tell in the dark, but it looks to be about the size of an apple.

The other two nod, and the tall one throws it through the window - literally. Glass and screen aren't barriers to the object's progress; they might as well not even exist. There's a pause, in which the children can be heard counting down - "Three, two, one..."

Then there's a bright flash of purple light and a woman's scream, followed instantly by mad cackling by the children, who jump-fall off the wall and race back for the street. "Happy Halloween!" they call over their shoulders.