It’s a joy to witness the seemingly miraculous transformation of a helpless newborn into an active, curious child and, ultimately, a capable and independent adult. No two children develop in exactly the same way, but the phases of child development are, for a healthy child, logical and predictable.

There is plenty that parents can do to support their child’s optimal development, but there’s no advantage to rushing it, says Joseph Woolston, MD, a Yale Medicine Child Study Center psychiatrist.

According to Dr. Woolston, child development is “a complex unfolding of a series of skills and adaptations, with very predictable stages, that occur in multiple dimensions at approximately the same time and in approximately the same order.” To assess whether an infant or child is developing at a healthy and normal pace, pediatricians and child development experts look at four domains (or aspects) of development:

• Motor skills, including large (or gross) motor skills, such as rolling over, crawling and learning to walk and run, and fine motor skills, such as the ability to pick up and eat small pieces of food or hold a pencil and draw or write
• Sensory skills, including how a child uses the senses (taste, smell, touch, sound and sight) to learn about the environment
• Social skills, including how an infant interacts with parents and caregivers, and then with others, including siblings, extended family and strangers
• Cognitive skills, including how a child’s attention, memory, and thinking and learning skills develop and grow

Dr. Woolston says there is logic in how the developmental process unfolds. The visual recognition of parents’ faces, for example, starts social development, such as smiling, and cognitive development, in that the infant develops memory of parents as trusted caregivers. He points out that all this serves specific needs. “It’s no accident that stranger anxiety typically begins to occur as a child learns to walk and run,” he says. “Now that the child has the ability to move away from his mother, it makes sense from an evolutionary perspective that he needs to have anxiety triggered by a person who is not his mother.”

Child development begins in the womb. Here is an overview of the developmental phases that a typical, healthy child moves through in the first five years of life.

• Gestation, from conception through birth: The health of a growing fetus is shaped by genetics and environmental factors, including nutrition and exposure to toxins and infection. This period is important psychologically to parents who are adjusting to a new identity and set of responsibilities, Dr. Woolston says.
• Neonatal, during the first few months of life: “Some people call this the fourth trimester,” Dr. Woolston says, noting that development during this period is focused on attunement, to the baby’s body (feeding, sleeping, elimination of waste) and to the primary caregiver. “This is when babies begin to show both visual and facial expression reciprocity,” he says.
• 4 to 18 months: Social (babbling, laughing) and sensory (taste, sight, sound) skills become more complex. Babies begin to control their limbs and bodies, learning how to use their hands and wave their feet—precursors to being able to walk. Cognitive skills, such as memory, sharpen. “This is the phase when the baby and primary caretaker should be developing a very robust attachment,” Dr. Woolston says. “Toward the end of this phase, the baby understands that just because someone or something is out of sight doesn’t mean it is ‘gone’ forever.”
• Toddlerhood: Learning to walk (or “toddle,” as it used to be said) gives a child increasing autonomy, Dr. Woolston says, noting that the newfound ability to say “no” is a way to test limits and establish boundaries.
• Preschool: Ages 3 to 5 are a “wonderfully exuberant time of life,” Dr. Woolston says. Mastery of more complex social skills allows children to make friends, engage in creative play and understand humorous concepts such as irony and upside-down.

Each phase includes what Dr. Woolston describes as “a suite of skills clustered together to form a stage of competency—motoric, sensory, cognitive and, most important of all, social. Humans are social primates. Human development is all about our progressive capacity for more and more complex social development.”

Proud parents naturally share information about what their children are doing. Many feel proud when a child masters a particular skill (such as putting together a sentence) on the early end of a developmental phase and/or worried if another milestone (such as walking) happens on the later side. But neither is all that meaningful. What matters is that these milestones occur within the normal range.

Pediatricians evaluate basic developmental progress in the routine well-child visits. It’s not always linear: Many kids regress a bit, here and there, before moving on to new accomplishments. A healthy child may be late to walk, for example, but if all else is well, there’s little reason for concern.

On the other hand, if a child shows a pattern of delayed development, there may be a problem and an assessment may be in order. 

“Children are motivated to move forward in their development and master their world,” says Ann L. Close, PhD, associate director of the Child Study Center's Infancy & Early Childhood Program and a specialist in the assessment and treatment of children under 5. “We worry when there’s no drive toward progressive development. There can be a number of reasons for this, but we want to know what they are so we can help the child get back on track.”

At the Child Study Center, a developmental assessment includes a thorough examination of a child’s medical and developmental history, starting with information about the mother’s pregnancy. Evidence-based diagnostic tests (such as the Bayley Scales of Infant and Toddler Development and the Mullen Scales of Early Learning) are used to determine whether there is a meaningful delay, identify it, and measure its extent. Specialists from other disciplines, such as speech and language, may be called in to evaluate, and school or childcare visits may be part of the process, too. Data on a child’s mastery of language, motor skills and cognitive, social and emotional development are used to arrive at a diagnosis and a treatment strategy, which are shared with the parents at a feedback session.

Treatment for developmental delays will vary according to the age of the child and the diagnosis. For example, for very young children, treatments may consist of state-financed home visits as part of the Birth to Three program and therapeutic interventions, such as speech and language, occupational or physical therapy. School-age children will require the development of a special education plan designed to address the specific needs of the child. 

The Yale Medicine Child Study Center has played an important role in the field of child mental health, contributing groundbreaking research and innovative ideas that have changed and continue to shape national policy, says Linda Mayes, MD, director of the center. “Deep policy considerations that relate to the health and wellbeing of children, such as universal preschool, are part of our history here,” she says.

The Child Study Center is committed to looking at child development in the context of the “whole child,” Dr. Mayes says. “If a child comes to us with a speech and language delay, we are not necessarily trying to hone down to one diagnosis,” she says. "Speech services might be an outcome that we’d arrive at, but we’d also be looking at the family. We’d bring together speech and language specialists, developmental pediatricians, and others. When we obligate ourselves to help a family, we are there with them for as long as they want us.”

“There is no such thing as ‘standard of care’ here,” Dr. Mayes says. “We have no hard standard of ‘normal’ that we expect all kids to adhere to. We’re really about the full context of a child and what is holding back or of concern to his or her family and their definition of success and health.”

The emphasis at the Child Study Center is, she says, “the best interest of the child.”

“We take an adaptive point of view,” she says. “We want to know what serves this particular child’s best interests in keeping development on track. We don’t lose sight of the child or the parents. Our goal is to help them have stability in their lives.”