Parents can treat an infant's constipation by trying a different formula brand, adding prune or pear juice to formula, or giving 1 to 2 ounces of water per day to an infant over four months old, according to WebMD. An infant is constipated if he has hard stools.
Painful bowel movements may indicate constipation in an infant, explains Mayo Clinic. He may arch his back, cry or tighten his buttocks during bowel movements. Constipation often starts when the infant starts solid foods. Feeding the baby pureed prunes, peas or barley cereal can alleviate constipation. Parents can use glycerin suppositories if the infant struggles to have a bowel movement. Parents should contact a doctor if the infant also vomits or experiences rectal bleeding.