Why you don't let 3 year olds name things

We asked Melody what she would like to name her new baby brother or sister. Without hesitation, she says, "Light Stick" Not sure where that came from, but she won't call the new baby anything else. And I hate to say it, but it's funny enough that it's starting to catch on. I've recently convinced her that we can't name the baby Light Stick, but she may call it that if she wants.