You're definitely on to something with your thoughts about the conflict being about the characters. You could certainly make the case that Heathcliff's conflict with Catherine stems from class, but is exacerbated by the way that Heathcliff is treated by Catherine and by Edgar. Heathcliff is most effected by the fact that Catherine chooses Edgar over him. But she chooses Edgar because of his status, so there's the class issue again. You might say that Heathcliff's attitude and personality are developed because of the way he was treated. It's jealousy that make Hindley treat him so poorly and I think that's where he gets his weird, evil ways. They ARE kids when all this starts, but I think kids are certainly aware of class. However, Hindley is jealous because Heathcliff is the new kid in town.