what qualities does charlie have that make him the hero of the story ? Or what do those qualities say about Roald Dahl opinion of children ?

Unlike the other contestants who find a Golden Ticket, Charlie is generous and selfless. He is the only one who would have been fit to run the factory. Even when he drank the Fizzy Lifting Drink, he admitted it and apologized, in a situation where lesser children might have lied and not owned up to their misdeeds. At the end of the story, Wonka bequeaths the factory to Charlie, as a reward for his good heart. His whole family is allowed to come with him.