Physical Development
In infancy, toddlerhood, and early childhood, physical development occurs rapidly. Understanding growth patterns helps caregivers and healthcare providers monitor healthy development.
Newborn Size and Growth Patterns
- At birth: Newborns typically weigh between 5 and 10 pounds, with an average of 7.5 pounds (3.4 kg). Average length is 19.5 inches (49.5 cm).
- First year: A newborn’s weight doubles by 6 months and triples by 12 months. Length increases to 29.5 inches (75 cm) by the first birthday.
- Second year: By age 2, weight has quadrupled from birth. A 2-year-old typically weighs between 20 and 40 pounds (9-18 kg) and measures 34.4 inches (87.5 cm) (WHO Multicentre Growth Reference Study Group, 2006).
Infant Reflexes
Although small, newborns are not helpless. They come equipped with reflexes and sensory capacities that help them interact with the environment from birth.
What Are Reflexes?
Newborn reflexes are inborn automatic responses to particular forms of stimulation. These reflexes help infants survive until they can perform more complex behaviors voluntarily. Present in babies with normally developing brains, most reflexes disappear around 4–5 months as the brain matures and voluntary motor control develops.
key newborn reflexes
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Rooting reflex: When you stroke a baby’s cheek, they naturally turn their head in that direction and begin to suck. This helps the infant locate a food source.=
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Sucking reflex: Infants automatically make sucking motions when the oral region is stimulated or an object is placed in the mouth. This reflex coordinates with breathing and swallowing for feeding.
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Grasping reflex: When you place your finger in a newborn’s palm, the baby automatically grasps it. This palmar grasp appears when anything touches the infant’s palm.
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Moro reflex: When infants feel like they’re falling (such as when their arms are released after being pulled up), they spread their arms, pull them back in, extend their fingers, and usually cry. This protective response to disrupted body balance develops by 28 weeks gestation and disappears by 6 months.
Clinical Significance of Reflexes
Recent research has highlighted the importance of primitive reflexes in assessing neurological development. According to 2023 research, these reflexes serve as important assessment tools in newborns and young infants. The presence and appropriate disappearance of reflexes indicate normal central nervous system development (StatPearls, 2023).
Retained primitive reflexes (when reflexes don’t disappear as expected) can indicate developmental concerns. A 2025 study found that non-integrated primitive reflexes in children can lead to motor function issues and psychological challenges. Research shows that 12-week intervention programs can reduce retained reflexes and improve motor and cognitive performance (Frontiers in Psychology, 2025).
Connection to later development: Emerging research suggests that primitive reflexes may influence later skills. For example, retained reflexes have been linked to difficulties with:
- Motor skill development
- Cognitive processing
- Speech and language development
- Executive function
Healthcare providers use reflex assessment as part of neurological screening, with tools like the Brazelton Neonatal Behavior Assessment Scale evaluating reflex strength alongside environmental responsiveness.
Infant Sensory Abilities
What can young infants see, hear, and smell? Newborn sensory abilities are significant, though not yet fully developed. Many innate preferences facilitate interaction with caregivers.
Vision
Vision is the least developed sense at birth, but newborns already show preferences for faces. Babies just a few days old prefer:
- Human faces over other visual stimuli
- Human voices over non-speech sounds (Vouloumanos & Werker, 2004)
- Their mother’s voice over a stranger’s voice (Mills & Melhuish, 1974)
Supporting research: In one experiment, 3-week-old babies were given pacifiers that played recordings of either their mother’s voice or a stranger’s voice. When infants heard their mother’s voice, they sucked more strongly on the pacifier (Mills & Melhuish, 1974).
Smell
Newborns have a strong sense of smell. They can distinguish their own mother’s scent from others. In MacFarlane’s (1978) study, 1-week-old breastfed babies were placed between two gauze pads—one from a stranger’s bra and one from their own mother’s bra. More than two-thirds of the babies turned toward their mother’s scent.
Growth During the Early Years
During infancy and childhood, growth does not occur at a steady rate (Carel, Lahlou, Roger, & Chaussain, 2004).
- Growth slows between 4 and 6 years old: During this time children gain 5–7 pounds and grow about 2–3 inches per year.
- Once girls reach 8–9 years old, their growth rate outpaces that of boys due to a pubertal growth spurt. This growth spurt continues until around 12 years old, coinciding with the start of the menstrual cycle.
- By 10 years old, the average girl weighs 88 pounds, and the average boy weighs 85 pounds.
Brain Development
We are born with all the brain cells we will ever have—approximately 100–200 billion neurons (nerve cells) whose function is to store and transmit information (Huttenlocher & Dabholkar, 1997). However, the nervous system continues to grow and develop throughout childhood.
Brain size increases rapidly:
- Age 2: Brain is 55% of adult size
- Age 6: Brain is about 90% of adult size (Tanner, 1978)
- Early childhood (ages 3–6): The frontal lobes grow rapidly. These areas are associated with planning, reasoning, memory, and impulse control. By school age, children are developmentally capable of controlling their attention and behavior.
- Elementary school years: The frontal, temporal, occipital, and parietal lobes all grow. Brain growth spurts tend to follow Piaget’s sequence of cognitive development, so significant changes in neural functioning account for cognitive advances (Kolb & Whishaw, 2009; Overman, Bachevalier, Turner, & Peuster, 1992).
Blooming and then pruning occur.
- Blooming: During infancy and toddlerhood, each neural pathway forms thousands of new connections. This period of rapid neural growth occurs during the first few years of life.
- Pruning: Following blooming, neural connections are reduced through pruning. This process helps the brain function more efficiently, allowing mastery of more complex skills (Hutchinson, 2011). Pruning continues through childhood and into adolescence in various brain areas.
Motor Development
Motor development occurs in an orderly sequence as infants move from reflexive reactions (such as sucking and rooting) to more advanced motor functioning. Babies first learn to hold their heads up, then sit with assistance, then sit unassisted, followed later by crawling and walking.
motor skills
Motor skills refer to our ability to move our bodies and manipulate objects.
Fine motor skills focus on small muscles in fingers, toes, and eyes. They enable coordination of small actions such as:
- Grasping a toy
- Writing with a pencil
- Using a spoon
Gross motor skills focus on large muscle groups controlling arms and legs. They involve larger movements such as:
- Balancing
- Running
- Jumping
Average Milestones
There are certain developmental milestones that young children typically achieve as they develop (Table 1). For each milestone, there is an average age, as well as a range of ages in which the milestone should be reached. An example of a developmental milestone is sitting. For example:
- On average, most babies sit alone at 7 months old. Sitting involves both coordination and muscle strength, and 90% of babies achieve this milestone between 5 and 9 months old.
- On average, babies are able to hold up their heads at 6 weeks old, and 90% of babies achieve this between 3 weeks and 4 months old.
If a child displays delays on several milestones, parents or caregivers should discuss this with the child’s pediatrician. Some developmental delays can be identified and addressed through early intervention.
| Age (years) | Physical | Personal/Social | Language | Cognitive |
|---|---|---|---|---|
| 2 | Kicks a ball; walks up and down stairs | Plays alongside other children; copies adults | Points to objects when named; puts 2–4 words together in a sentence | Sorts shapes and colors; follows 2-step instructions |
| 3 | Climbs and runs; pedals tricycle | Takes turns; expresses many emotions; dresses self | Names familiar things; uses pronouns | Plays make-believe; works toys with parts (levers, handles) |
| 4 | Catches balls; uses scissors | Prefers social play to solo play; knows likes and interests | Knows songs and rhymes by memory | Names colors and numbers; begins writing letters |
| 5 | Hops and swings; uses fork and spoon | Distinguishes real from pretend; likes to please friends | Speaks clearly; uses full sentences | Counts to 10 or higher; prints some letters and copies basic shapes |
The Importance of Play and Recess
According to the American Academy of Pediatrics, unstructured play is integral to child development. It builds creativity, problem-solving skills, and social relationships. Outdoor play offers additional benefits by allowing children to directly experience the world around them. Through outdoor play, children may collect objects that spark lifelong interests, increase their exercise levels, and develop greater enjoyment of physical activity—all supporting healthy heart and brain development.[1]
Physical activity is crucial for preventing childhood obesity, yet recent data reveals concerning trends. About 1 in 5 American children (19.7%) have obesity (CDC, 2022). This represents an increase from earlier years and affects millions of children nationwide.
Childhood obesity results from multiple factors, but two stand out:
- Reduced physical activity: Less than 20% of the world’s adolescent population is sufficiently physically active.[2]
- Only 16% of children walk or bike to school today compared with 42% in the late 1960s.
- Recess and unstructured playtime has declined. As of the 2024-2025 school year, only 10 states require a minimum amount of daily recess for elementary schools. Requirements vary widely—Arkansas requires the most at 40 minutes daily, while Louisiana requires only 15 minutes. Most U.S. elementary schools (83%) provide daily recess, but only 21% offer two periods of daily recess.[3]
- Poor nutrition: Easy access to calorie-dense, nutrient-poor foods creates an imbalance between energy intake and expenditure
Children with obesity face elevated risks for numerous health problems:
- Physical health: Asthma, sleep apnea, bone and joint problems, type 2 diabetes, and high blood pressure
- Mental health: Depression and anxiety. Childhood obesity is also linked to abnormalities in brain structure, particularly in regions associated with executive functioning. These brain areas control cognitive flexibility, inhibitory control, planning, working memory, and decision-making—all essential for daily activities, academic success, and social relationships (Mora-Gonzalez et al., 2019).
- Long-term risks: Obesity typically persists into adulthood, increasing risks for cardiovascular disease, cancer, and premature death
Despite evidence showing the importance of physical activity and play, several barriers prevent children from getting adequate exercise, including overscheded structured activities and policies that have reduced or eliminated recess to allocate more time for test preparation.
A 2022 survey found that 86% of teachers in the U.S. have decreased or taken away recess as punishment for behavior. A 2022 longitudinal study found that withholding all or part of recess to punish misbehavior or finish classwork is directly related to increased sedentary behavior and decreased physical activity—the opposite of what children need for healthy development.
Critical thinking question: Do you agree with these practices? Why or why not? Consider how eliminating recess might affect children’s physical development, cognitive functioning, attention spans, and overall well-being. What alternative approaches might schools take to support both academic achievement and physical health?
- Centers for Disease Control and Prevention. (2025). Preventing childhood obesity: 6 things families can do. https://www.cdc.gov/obesity/family-action/index.html ↵
- Wyszyńska, J., Ring-Dimitriou, S., Thivel, D., Weghuber, D., Hadjipanayis, A., Grossman, Z., ... & Mazur, A. (2020). Physical activity in the prevention of childhood obesity: The position of the European Childhood Obesity Group and the European Academy of Pediatrics. Frontiers in Pediatrics, 8, 535705. ↵
- Howie, E. K., Harden, S. M., Barr-Anderson, D. J., & Long, C. R. (2025). Elementary school compliance with a state recess minimum requirement by racial and geographic factors: a cross-sectional study. The international journal of behavioral nutrition and physical activity, 22(1), 37. https://doi.org/10.1186/s12966-025-01730-x ↵