Following birth, an infant's length increases significantly, reaching an average of 29.5 inches by 12 months and 34.4 inches by the age of two.

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From infancy to childhood, individuals develop:
- Reflexes
- Motor Skills

Physical Development from Infancy to Childhood

Spielman, R. M., Jenkins, W. J., & Lovett, M. D. (2020, April 22). Psychology (2nd ed.). OpenStax. https://openstax.org/books/psychology-2e/pages/1-introduction

OpenStax Psychology (2nd ed.) Textbook

Newborn reflexes are inborn, automatic responses to specific forms of stimulation that are crucial for a baby's survival. These reflexes, which are present in all healthy infants with normally developing brains, help them interact with their environment from birth until they can perform more complex behaviors. Typically, these reflexes fade and disappear by the time a baby is around 4 to 5 months old.

Newborn Reflexes

Motor skills are abilities that enable individuals to move their bodies and manipulate objects. These skills are generally classified into two main categories: fine motor skills, which involve small, precise movements, and gross motor skills, which involve larger movements using major muscle groups.

Motor Skills

Adenarche

Gonadarche is a key physical change during puberty characterized by the maturation of the sex glands (gonads).

Gonadarche

The average weight for a newborn at birth ranges from 5 to 10 pounds. A typical weight is often cited as around 7.5 pounds.

Average Newborn Weight

From the moment of birth, newborns are equipped with sensory capacities that, along with their reflexes, enable them to begin interacting with their environment. These innate abilities are fundamental for their initial engagement with the world.

Newborn Sensory Capacities

The average length of a newborn baby at birth is 19.5 inches.

Average Newborn Length

Length Development in Infancy and Early Childhood

A visual representation of rapid physical growth from birth to early childhood is shown through a series of four photographs. The images display a child's progression, starting with a sleeping newborn, followed by a toddler with a toy giraffe, then a baby celebrating what appears to be a first birthday by blowing out a single candle, and finally, a young child playing on a swing.

Image Collage Illustrating Physical Development from Infancy to Childhood

Physical growth during infancy and childhood is not a constant process; it is characterized by periods of acceleration and deceleration rather than occurring at a steady rate.

Non-Steady Growth Rate in Childhood

Infant motor development follows a predictable and orderly sequence, progressing from initial reflexive reactions, such as rooting and sucking, toward more sophisticated motor abilities. This progression generally begins with infants learning to hold their heads upright, followed by sitting first with support and then independently, before eventually advancing to crawling and walking.

Sequence of Infant Motor Development

Analyze the behaviors described in the case study below. Identify and differentiate between the two primary categories of motor skills the child is demonstrating, providing a specific example of each from the text.

Analyzing Motor Skill Development

During early childhood, the physical size of the brain increases rapidly. A 2-year-old's brain is approximately 55% of its adult size, and by the age of 6, it reaches about 90% of its adult size (Tanner, 1978).

Brain Size Growth in Early Childhood

Between the ages of 3 and 6, the frontal lobes of the brain grow rapidly. Because the frontal lobes are associated with planning, reasoning, memory, and impulse control, this rapid growth means that by school age, children become developmentally capable of controlling their attention and behavior.

Frontal Lobe Growth in Early Childhood

Throughout the elementary school years, the brain continues to develop physically as the frontal, temporal, occipital, and parietal lobes all increase in size.

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