Nah, what's childish is the exact opposite. Children don't mind having everything spoiled for them, because it means they get to see / hear about all the cool stuff immediately. Instant gratification is a child's game. Delayed gratification, such as that which comes with suspense and mystery, is something you grow to appreciate. You're an asshole if you spoil things for others.
edit: Children also don't mind spoiling things for others. They have no concern for spoilers.