Most Helpful Guy
Is that all? Like, he catches the urchin and gives him some bad noise and then there's a twist and that's your story? That's REALLY short.
Is there any backstory, here? Like, why's he picking pockets, what's going on?
One angle could be; the kid is some lowly Romanichal gypsy, or something, who's been lifted and taken in by this Child Groomer who keeps a fetish of kids in his old house, and does terrible lecherous things to them, and makes them go out pick-pocketing.
So, in media res, kid is picking the pocket of the officer, officer catches him, gives him bad noise and takes him down to the station to find out who his parents are or whatever. So he's sitting down at the pen while the officer is making phone calls, and then he's taken into another room. The kid starts having memories, like the initial memories, the set-up, to being lifted from his gypsy lifestyle and taken in by the terrible child groomer, and made to go pick-pocketing. Then everyone knows the story. Then, the officer comes out and lets him go, and he trots on home to the Place where he lives, back to the groomer.
And then, whaddaya know, the child groomer is wearing a big top police uniform, and we overhear a conversation between him and some politician, telling him he's gonna get caught on if he keeps releasing all the kids, and he tells him 'I'm economising enough - I'm just rescuing my favourites, now.' or whatever. And then the kid slinks back and has no idea what's going on, really, and nothing changes.
Twists suck, though, all twists are really bad.