Newborns are infants who are just born, typically defined as being from birth to 28 days old. During this time, they undergo rapid physical and developmental changes. Newborns usually weigh between 5.5 to 10 pounds and measure about 18 to 22 inches in length. Their senses are developing, and they can recognize their mother's voice and smell. In the early days, newborns spend most of their time sleeping, waking only to feed. They require frequent feedings, usually every 2 to 3 hours, as their stomachs are small. Care for newborns includes regular check-ups with a pediatrician to monitor their growth and health.