Take Action

Join the movement of young people working to protect our health and lives

Action Center

Take action to help ensure young people's health and rights.


Donate now

Support youth activists working for reproductive and sexual health and rights.


Sign up

Get text and email updates


Growth and Development, Ages Zero to Three-What Parents Need to Know

Download this information (pdf)

Order publication online.

Also available as PDF in

Human development is a lifelong process of physical, behavioral, cognitive, and emotional growth and change. In the early stages of life—from babyhood to childhood, childhood to adolescence, and adolescence to adulthood—enormous changes take place. Throughout the process, each person develops attitudes and values that guide choices, relationships, and understanding.

Sexuality is also a lifelong process. Infants, children, teens, and adults are sexual beings. Just as it is important to enhance a child’s physical, emotional, and cognitive growth, so it is important to lay foundations for a child’s sexual growth. Adults have a responsibility to help children understand and accept their evolving sexuality.

Each stage of development encompasses specific markers. The following developmental guidelines apply to most children in this age group. However, each child is an individual and may reach these stages of development earlier or later than other children the same age. When concerns arise about a specific child’s development, parents or other caregivers should consult a doctor or other child development professional.

Physical Development

Most children aged zero to three will:

  • Double their height between birth and age three
  • Triple their weight between birth and age three
  • Develop teeth and the ability to eat solid foods
  • Develop 75 percent of their brain capacity
  • Learn to crawl and walk
  • Develop large motor skills such as running, jumping, and climbing up stairs
  • Begin to take off and put on clothes
  • Begin to control body functions through toilet training

Cognitive Development

Most children aged zero to three will:

  • Learn language and communication skills and advance from using single words to phrases to complete sentences
  • Develop an imagination and begin to create imaginary scenarios and friends
  • Understand the world primarily through their family
  • Begin to interact with peers through imitation [Although some children at this age do not yet play directly with each other, they often engage in parallel play.]
  • Think concretely, retain some information, and process information primarily through their five senses—by seeing, touching, hearing, tasting, and smelling
  • Identify with and begin to imitate their same-sex parent or guardian
  • Begin to understand the differences between male and female (gender differences and gender roles)
  • Imitate the language and behavior of trusted adults

Emotional Development

Most children aged zero to three will:

  • Develop trust for caregivers who fulfill their needs, such as responding when the child is hungry, wet, etc.
  • Begin to test independence and explore limits, but still seek closeness to primary caregiver
  • Have relationships primarily with family members who are the most important people in the child’s life at this time
  • Physically demonstrate feelings, such as kissing and hugging to show love and hitting to show anger
  • Master the idea of being happy, sad, or angry, but will generally choose to express emotions physically rather than verbally [The “terrible twos” occur when a child is developing a sense of self outside of and distinct from others, and expresses this individuality by saying “no” and by insisting on doing things him/herself.]

Sexual Development

Most children aged zero to three will:

  • Be curious and explore their own body and others’ bodies
  • Experience an erection or vaginal lubrication
  • Touch their genitals for pleasure
  • Talk openly about their bodies
  • Be able to say and understand, when taught, the appropriate names for body parts (head, nose, stomach, penis, vulva, etc.)

What Families Need to Do to Raise Sexually Healthy Children

To help children ages zero to three to develop a healthy sexuality, families should:

  • Help children feel good about their entire body. Caregivers should name all body parts accurately and convey that the body and its functions are natural and healthy.
  • Touch and comfort children often to help them understand love and how it can be shared. Meeting children’s needs also helps them develop trust.
  • Help children begin to understand the difference between public and private behaviors and that certain behaviors, such as picking one’s nose or touching one’s genitals, are private ones.
  • Teach about anatomical differences between males and females while maintaining that boys and girls are equally special.
  • Teach children that they can say no to unwanted touch, regardless of who is attempting to touch them, and that they have a right to be respected when they say no.
  • Describe bodily processes, such as pregnancy and birth, in very simple terms.
  • Avoid shame and guilt about body parts and functions.

Sign up for Updates