Pediatricians must monitor early breastfeeding to detect and manage breastfeeding difficulties that lead to slow weight gain and subsequent low milk production. Infant growth during the first 3 months of life provides a clear indication of breastfeeding progress. Healthy, breastfed infants lose less than 10% of birth weight and return to birth weight by age 2 weeks. They then gain weight steadily, at a minimum of 20 g per day, from age 2 weeks to 3 months. Any deviation from this pattern is cause for concern and for a thorough evaluation of the breastfeeding process. Evaluation includes history taking and physical examination for the mother and infant. Observation of a breastfeeding session by a skilled clinician is crucial. A differential diagnosis is generated, followed by a problem-oriented management plan. Special techniques may be used to assist in complicated situations. Ongoing monitoring is required until weight gain has normalized. In most cases, early intervention can restore promptly infant growth and maternal milk supply. Underlying illness of the infant or mother must be considered if weight gain and milk supply do not respond to the earlier-mentioned interventions as expected. Physicians are responsible for knowledge about additional resources and for coordination of breastfeeding care. Pediatricians have a pivotal role in achieving the goals of optimal breastfeeding and appropriate infant growth.