Your toddler's been doing fine, and all of a sudden she wails when you go to leave. It's common for separation anxiety to rear its head again at about 18 months. Truth is, you may be more upset by her farewell fussing than she is. Want to know a secret? Most toddlers calm down within a few minutes after their parent leaves. Make a fast good-bye and promise her you'll be back to pick her up. It may seem scary, but many toddlers bang their heads to comfort or stimulate themselves, or to release frustration. Don't let it worry you too much. On the other hand, if the head banging goes along with social problems -- for example, if your child rarely looks directly at you and doesn't seem to want to play with you -- or if it's been going on for a long time, there may be cause for concern. Check with your pediatrician.