Final answer:
Newborns primarily use brown adipose tissue to generate heat through nonshivering thermogenesis because of their faster heat loss due to a larger surface area to mass ratio.
Step-by-step explanation:
The primary means of heat generation in the first three months of life is brown adipose tissue. This specialized tissue, found in newborn infants and young children, notably at their neck and the backside of their trunk, helps in thermoregulation through the process of nonshivering thermogenesis. Unlike adults, infants have a thin layer of subcutaneous fat, offering less insulation against heat loss. Brown adipose tissue, rich in mitochondria and possessing a unique protein that allows for heat generation without ATP production, breaks down to produce heat when a newborn is exposed to cold. This heat production is crucial because newborns lose heat more rapidly due to their larger surface area to mass ratio.