Physical development includes brain growth, skeletal growth, muscle development, coordination, and development of gross and fine motor skills. There are many physical changes that take place during a child’s first 3 years of life. For example, newborn babies, who are relatively immobile, will begin to roll over in just a few months and eventually start their journey of moving about the world.

We can witness physical changes of the body by observing how the child fits into their clothing or by the way the child is able to move independently. Other changes happen within the complex structures of the brain. While we cannot see this transformation happen, we certainly notice it when babies start to engage in increasingly advanced tasks, such as crawling and walking. Let’s take a look at what’s happening in a child’s early physical development by examining the growing body.

5.14.1 The Growing Body

The body grows through dramatic physical changes in the first several years of life, starting first with the brain and head. A young child’s head is relatively big compared to the rest of their body. The head initially makes up about 50 percent of the body’s length when we are developing in the womb. At birth, the brain is 25% of its adult size, 75% by age 1 and 80% by 3 years of age (Graber, 2023). Children literally grow into their heads!

Infant’s have a difficult time holding their head up due to immature neck muscles (and their large heads). As they start to explore their bodies and attempt to move around, the neck muscles eventually become strong enough to support other movements. Infants can usually hold their heads up at around two months old, especially if they are given tummy time, which is the practice of placing an infant on a flat surface on their stomachs during awake times. The World Health Organization recommends that infants get at least 30 minutes of tummy time daily (WHO, 2022).

Newborn reflexes will switch from automatic responses to those of intention. Infants develop strong sensory responses which then prompt physical responses to stimuli within the environment. For example, a caregiver may place a baby on a play mat with several hanging pieces on it. At first, the infant may only be able to observe the pieces. Eventually, they will be able to grab or swat at them. These seemingly simple actions are important in the overall development of a child’s physical skills.

Infants experience quick body growth in the first year of life. For example, they will see an increase in body length of 30% by 5 months old and more than 50% by a year old (Graber, 2023). Children’s bodies will continue to be characterized by big heads, curved backs, and a protruding belly. They have short arms and legs and may appear bow-legged (Lee, 2023; Graber, 2023). By 3 years of age, children will have more proportionate bodies as they gain more muscle and grow taller.

A big change that is occurring within a child’s body is the ability to control the muscles associated with potty training. “Most children develop control over their bowel and bladder by 18 months” (Zero to Three, 2010). A child’s physical capabilities are important in potty training but a child may not be emotionally ready to handle potty training. Toddlers are becoming increasingly independent and demonstrate the need for control over their bodies. Potty training should be a natural part of their learning process in order to avoid infamous toddler power struggles. Children may decide to exert control over their bodies by not going to the potty when needed which can lead to some physical issues such as constipation (Zero to Three, 2010).

There are many factors that impact a child’s physical development. Genetic and heredity traits are passed from parents to children which can influence the way a body is constructed and developed. Environmental factors such as toxins or teratogens can also impact whether a child’s brain and body develop as expected. A child’s access to healthy and consistent nutrition influences whether a child acquires the vitamins and nutrients needed to support their brain and body growth. And most importantly, the types of interactions that infants and toddlers have with their primary caregivers serve as a foundation for healthy physical development.