I think it is the parenting. But that has nothing to do with how rich or poor the parents may be.
There is a 19 year old boy in my town that sells drugs, causes trouble, bothers elderly people by sitting outside their homes with music blaring at midnight - he is with others, but he is the ring leader. His parents own a huge property development company, he lives in a mansion with an indoor pool, and drives around in a brand new car that Mummy and Daddy bought him. He is not expected to work. So he just hangs about with other "kids", generally causing mayhem.
Also, a few boys beat a security guard up about a year ago - they almost killed him. In the foray one of the attackers had a designer cap ruined. What did his Mum do? Treated him to a new one.
Namby pamby parenting. Kids growing up in a society where adults don't say "no".
Of course, on the other hand, you do have the kids born in to abject poverty. Their parents are high on something and don't give 2 shits where the kids are, or what they're doing. Of course these kids will gravitate towards gangs, in order to belong somewhere. And then it's survival of the fittest. If you're not seen as "hard", you'll be picked on.
In both cases above, the parenting is to blame.
Either way, I'd lock these little shits up for 5 years minimum. See how "hard" they are in jail with some real hard criminals.