If they're 4th generation Mexicans, then wouldn't their kids be 1st generation Americans?
They were american citizens as were their parents, grandparents, etc. but they still weren't americans.
Their loyalty was to Mexico, they spoke spanish whenever they could get away with it, they had the same gangs that are present now except that they weren't as violent (knives, chanis, clubs, and very few guns and they fought other mexican gangs.
Their grnadkids have graduated to drug dealing, killing, vandalizing, and stealing but instead of beating up other gang members and rarely killing them they now resort to killing and not just by guns. They hydraulic them (putting them under a low rider and bouncing the air bags up and down until their victim is smashed to death or tying them to the telephone pole and smashing them with the bumper of a car until they reach their chest and the smashing kills them.
I wasn't rare to go to my office on a Saturday morning and find one of them dead in the middle of the street.