Short answers, pulled from the story.
A baby is the very young offspring of adult humans, and infant, which literally means unspeaking, is a formal or specialised synonym. In medical contexts a neonate is an infant in the first 28 days after birth, applying to premature, full term, and postmature infants. The term infant typically applies to children under one year of age, though some definitions extend it to two years.
In developed countries the average total body length of a newborn ranges from 35.6 to 50.8 centimeters, and the average birth weight of a full-term newborn is approximately 3.4 kilograms, typically 2.7 to 4.6 kilograms. Normal head circumference for a full-term infant is 33 to 36 centimeters. Premature newborns may be much smaller.
At birth many regions of a newborn's skull have not yet been converted to bone, leaving soft spots called fontanels. The two largest are the diamond-shaped anterior fontanel at the top front of the head and the smaller triangular posterior fontanel at the back. A protein called noggin is responsible for the delay in the skull's fusion, which completes naturally later in life.
A 2013 study found infants carried by a walking mother calmed significantly, while those left in a cradle cried, kicked, and had an increased heart rate. Infants who received positive touch such as stroking cried less and smiled more, while negative touch has been linked to later emotional and behavioral problems. A 1986 randomized study showed carrying makes infants more content and cry less.
Infants begin language through babbling, and a prompt parental response to that babbling leads to faster language acquisition. Researchers who studied mothers of 8-month-old infants and tested vocabulary at 15 months confirmed this. Babies learn that sounds attach to objects when a parent comments as the baby looks at and babbles toward something, but only positive reactions promote language development.
Major causes of infant mortality include dehydration, infection, congenital malformation, and SIDS, and the rate is measured as deaths per 1,000 live births. It is recognized as an important measure of a country's health care, with wealthy nations such as Canada, the United Kingdom, the United States, and Japan showing low rates. In the United States the average is 6.8 per 1,000 live births, reaching 13.63 among non-Hispanic black women versus 5.76 among non-Hispanic white women.