And these aren't really hardened criminals. They are kids who make bad choices. For example: "One recruit described in news reports as a bomber actually was a young person who blew up a mailbox using a soda bottle full of gunpowder".
Hey, I blew things up when I was young, but never anything that didn't belong to me, so I didn't get in trouble.
They generally don't hand out serious felony convictions for minor little reasons or simply making, "bad choices".
To receive a felony charge, and be convicted of a felony, generally means you were involved in a serious crime.