I'm not sure about the Catholic teaching part, but Satan likes to ape God. Think of the legions of devils that must exist if he made a guardian angel for each soul before they were even created. Then think about the number of other choirs of angels that exist, and that a third of the entire number were cast into Hell.
It would make sense that each of us has a "guardian devil" that the devil has sent along with each one of us. There would be enough of them, to be sure.
One of my friends suggested that this is the case several years ago, and that the reason children fight, is because of those "guardian devils" following them around are helping provoke such tiffs. When the children go home after a visit, the devils are still harassing them.
I don't think there's any solid Catholic teaching on such things, but something like this would make total sense.