Involuntary urination during sleep; also known as nocturnal enuresis. Bed-wetting is common and normal among preschool children, with more than a third of 3-year-olds wetting the bed at night. By age 5, most children are able to control their bladders while sleeping. Bed-wetting is more common in boys than girls. Primary enuresis means the child has never been dry at night. Secondary enuresis refers to the child who has been consistently dry for a number of months before wetting the bed again.