A children's novel with a hardboiled narrator and prison slang? I'm there.
Harry Sue by Sue Stauffacher is about a tough as nails girl desperate to get "sent up" so she can join her mother behind bars. She lives with her grandmother, who runs what is quite possibly the most negligent daycare center in the world, and spends a good bit of her time defending Grandma's charges (aka "the crumb snatchers") from her. This interferes with Harry Sue's JD aspirations, as does her particularly good heart.
Maybe it's just me, but this sounds (potentially) like a cross between Louis Sachar's kiddie jailbreak tale, Holes, and Rian Johnson's high school noir, Brick.
Here's a little snippet:
"Time was running out on my becoming a juvenile delinquent. The really impressive cons started their rap sheets by nine or ten. Unfortunately, I had a heart condition that needed fixing before I could begin a serious crime spree.
Yes, Fish, my heart was as lumpy and soft as a rotten tomato. I couldn't stand to see things hurt, especially anything weak and defenseless. Watching Jolly Roger and his road dogs pull the legs off a spider made me grind my teeth down worse than if I slept with a mouth full of sandpaper. When those boys clicked the little kids on the bus, I had to sit on my hands just to keep from breaking theirs.
In the joint, where I was headed, I'd need a heart filled with cement and covered in riveted steel. I was working on it. But so far, I wasn't making much progress."
Thanks to Leila at Bookshelves of Doom for pointing this one out as her Recommendations from Under the Radar pick.