What is the primary characteristic of physical development during infancy?

The primary characteristic of physical development during infancy is the rapid growth in height and weight. During the first year of life, infants typically undergo significant changes, doubling their birth weight by around five months and tripling it by their first birthday. Additionally, they grow in height at an impressive rate, usually about 10 inches during the first year. This period of rapid physical growth is crucial for overall health and development and is essential for the formation of neurological connections that support later learning and functioning.

In contrast, improvement in fine motor skills occurs later in development, as infants gradually gain control over their movements. The development of secondary sexual characteristics is not a feature of infancy but rather a characteristic of puberty. Increased independence is also a trait that develops later in childhood as children grow and start to explore their environment more confidently. Therefore, the significant changes in height and weight during infancy clearly mark this developmental stage.