Final answer:
In the initial years of life, a baby's size and physical development undergo significant changes. This includes weight and length tripling and doubling respectively, sensory development, and the emergence of teeth around six months of age.
Step-by-step explanation:
During the first year or two in a baby's life, the size and physical development will change greatly. Infancy is characterized by rapid growth where a baby usually triples their birth weight and doubles in length. Growth includes major changes in the body proportions, motor skills, and cognitive abilities. The development of newborns' sensory organs, such as vision, touch, and hearing, will also progress considerably.
Physical features like hair and skin will show notable transitions. A newborn may initially have a covering of fine hair called lanugo and a waxy substance called vernix, which typically disappears within the first weeks. Similarly, the soft spots on the skull known as fontanels, which allow the head to reshape for birth, eventually ossify. Moreover, the emergence of deciduous teeth usually begins around six months, a sign of ongoing development. Normally by the first birthday, significant motor, sensory, and cognitive skills have evolved, marking infancy as a time of incredible growth and change.