Hmm. This one's a little tricky. You might say that the other children are antagonists in Charlie and the Chocolate Factory. First, every Golden Ticket they find represents a Golden Ticket Charlie hasn't found. There's also the fact that in the end, we find out that Charlie has been secretly competing against the other children to win ownership of the factory.
But honestly, we find that argument a little less than convincing. After all, throughout the book, these kids don't really cause much conflict for Charlie – they're too busy causing trouble for themselves. Charlie's real conflict is that he's poor and hungry, and in the end, that's really no one's fault (although all those greedy people in the world certainly aren't helping matters).