knowstheworldChildermass noticed them during the territory claim for Lewisham, and he notices them around in the area soon thereafter, stirring up trouble. Street urchins. Gangs of boys. Not dissimilar to one of the gangs that he grew up in himself, all things considered. Having grown up in one of them, he knows that it's not just 'kids being kids', as he watches them work together to wreak their havoc.
There's no reason for him to interfere so Childermass merely watches. Takes note on what targets they're making, the techniques they use to stir up trouble. He doesn't really make anything of it one way or another until they cross into Lambeth and then Norrell flies into a tizzy. Orders flying around to fix this, Childermass, they must be stopped, this must be stopped! So Childermass does as he's told and heads out to investigate further. Discovering a pattern to their movements, and while he cannot track the source of who may be giving them their instructions, he does notice them associating with a certain woman on more than a few occasions to be coincidence.
Having been a child like them before, he knows that questioning them will be no help. But questioning her, on the other hand. It seems a bit more promising of a prospect. Nancy, he discovers her name to be. A streetwalker, as it turns out, although he could have pinned that from the promiscuous way that she dresses more than half the times he spots her. It's enough to give him an idea...
He takes the car this time. He knows what kind of an image it makes, that from the chrome plating to the leather seats it's practically dripping money. He makes certain not to seem like he's not too interested, that he cruises his way through the ladies on the street before he finds his way to Nancy, rolling down the window and tipping his hat at her as a way of beckoning her forth. "Ma'am..."