All the parenting handbooks tell you that most children start to stay dry through the night at about age three. Ask any pediatrician and he'll tell you that about that time, he suddenly starts hearing questions from worried parents about their children still wetting the bed at night. According to most pediatricians, though, it's not unusual for children to wet the bed long past that age. If your child is still wetting the bed at five, should you be worried? How about at eight? What if it's only once in a while? Here are some facts to help you decide if you should worry about your child