My guess is it's just an age thing, because the way we communicate with each other is terribly complicated, and it takes a significant amount of time to learn the nuances. For example:
1) We expect people to pick up things unsaid due to context. Young children don't have enough contextual exposure to guess them correctly.
2) One of the great difficulties of learning the English language is the heavy use of idioms and slang. We often say one thing and mean another.
Some of these examples in this thread, IMO, reflect these challenges. Like, when the teacher said, "I'm not going to help you," she left it to the child to assume that "on this task" was implied but unsaid.
