What happens when you flee the scene of a accident?

A couple of my buddies were sitting on the side of the road and one of them threw a hub cap under a pickup truck and it skidded out and caused a 3 car pile up. Both of my friends left after the driver of the pickup almost kicked the sh*t out of them. I'm pretty sure their description would have been given to the police so if the cops find them what do you think could happen to them? I live in Canada by the way and they're both under 19.