If babies had no idea about the world, they'd not cry for food, or comfort, or attention, or whatever the hell else babies get upset about. They get upset because their ideas are in conflict with what is reality. Children are often taught to shy away from things which the parent doesn't want them to learn about. Think the kids who are forbidden from learning science. From learning factual things that make the actual world they live in. They are taught that they may substitute opinion for fact. That choosing to believe a fiction about something outranks fact about it. They have been influenced and trained by anti-intellectualism to live a ignorant existence and believe that they are the enlightened ones.
They don't cry because they think "Well, I'm hungry. Let's cry and see if anyone hears me! Maybe they'll bring me food, too". They follow their instincts; it's later in life do they learn that they can eat on their own if they know there's food around. You'd cry of pain if someone was to stab you in the leg, and it doesn't matter if you know or have shielded yourself from knowing who stabbed you or what did they stab you with. Instincts and reflexes have nothing to do with ignorance, other than the fact that we can learn to override them if we find out why it might be useful to us. I agree with most of the second paragraph.If babies had no idea about the world, they'd not cry