It seems a lot of parents want to protect their children, and therefore lie to them about things that exist in the real world, as an attempt to somehow keep them in the baby phase for longer.

For reference, Paul Graham has an interesting essay on this, called The Lies We Tell Our Kids. In it, he mentions a theory that swear words, for example, are just a way to mark the speaker as an adult. From the essay: "There's no difference in the meaning of "shit" and "poopoo." So why should one be ok for kids to say and one forbidden?"