The medical name for not being able to control urination is enuresis. Nocturnal enuresis is involuntary urination that happens at night while sleeping that is not under the child's control, after the age when a person should be able to control his or her bladder.
In a lot of cases, stress can be associated with enuresis. It's not uncommon to feel stressed out during the teenage years and events such as divorce, the death of a friend or family member, a move to a new town and adapting to a new school and social environment, or family tension can be overwhelming for a child. This is seen twice as commonly amongst boys than in girls of the same age.
If your child is having trouble controlling urine at night, consult a psychiatrist to rule out the possibility of a medical problem and manage the problem effectively as it can be extremely embarrassing for a growing child.