There are many reasons why a child who usually has regular, soft bowel movements becomes constipated. The most common causes of constipation are:

• Switching a baby from breast milk to formula, especially during the first 2 to 3 weeks of life. You may need to add extra water to your baby's formula for several weeks until your baby is no longer constipated.
• Changes in diet, such as when a child starts eating more adult foods. Constipation may also occur if your child drinks an excessive amount of cow's milk. This happens most often in children younger than age 2.
• Low fluid intake. Sometimes the normal amount of fluid a child drinks is not enough, such as when the weather gets hot or the child increases his or her physical activities.
• Not taking the time to have a bowel movement. A child may be so interested in play that he or she ignores the need to have a bowel movement.
• Reluctance to use the bathroom. A child might become constipated when he or she is in a new environment, such as when traveling.
• Changes in daily routine, such as when traveling or after starting school.
• Medications. Many medications can cause constipation.

Most young children will not be able to describe the feeling of fullness (bloating), nausea, or mild rectal pain caused by trying to pass a hard stool. Parents may notice that the child is irritable, fussy, or has a bloated abdomen when he or she is constipated.

A new bout of constipation usually improves with home treatment and prevention.

In rare cases, constipation in a child may be related to another, more serious, health problem.