A toddler is a child approximately 1 to 3 years old, though definitions vary. The toddler years are a time of great cognitive, emotional and social development. The word is derived from "to toddle", which means to walk unsteadily, like a child of this age.

Normal vital parameters of toddlers

Blood Pressure (mmHg)	Systolic	80–110
	Diastolic	50–80
Heart rate (BPM)		90–140
Respiratory rate		20–40

Toddler development can be broken down into a number of interrelated areas. There is reasonable consensus about what these areas may include:

• Physical: growth or an increase in size.
• Gross motor: the control of large muscles which enable walking, running, jumping and climbing.
• Fine motor: the ability to control small muscles; enabling the toddler to feed themselves, draw and manipulate objects.
• Vision: the ability to see near and far and interpret what is seen.
• Hearing and speech: the ability to hear and receive information and listen (interpret), and the ability to understand and learn language and use it to communicate effectively.
• Social: the ability to interact with the world through playing with others, taking turns and fantasy play.

Although it is useful to chart defined periods of development, it is also necessary to recognize that development exists on a continuum, with considerable individual differences between children. There is a wide range of what may be considered 'normal' development. However, according to experts, there are specific milestones that should be achieved by certain ages and stages in life in order to properly grow and develop. Medical experts also point out that children develop in their own time and suggest that carers should not worry too much if a child fails to reach all the milestones for their age range. Premature birth or illness during infancy may also slow down a young child's development.

Below follows a rough breakdown of the kinds of skills and attributes which young children can be expected to have developed by different points during the toddler period. Citations for the information given are provided here.

Aspects	One year old	Months after first birthday	18 months old	Two years old	Two and a half years old
Physical and motor	Triple the birth weight Grow to a height of 50% over the birth length Have a head circumference equal to that of the chest Have one to eight teeth Pull to stand Walk with help or alone Sit down without help Bang two blocks together Turn through the pages of a book by flipping many pages at a time Have a pincer grasp Sleep 8–10 hours a night and take one to two naps	Walks well alone with wide based gait Creeps upstairs Builds with blocks Drinks from a cup, uses a spoon Enjoys throwing objects and picking them up	Walks sideways and backwards, runs well, falls easily Climbs stairs or up on furniture Scribbles vigorously, attempting a straight line Drinks well from a cup, still spills with a spoon	Weight: about 11–13 kg Height: about 80–82 cm Teeth: 12 temporary Gross motor skills are quite well refined, can walk up and down stairs on both feet with one step at a time while holding on to a rail Builds tower of five cubes Control of spoon well-developed Toilet trained during day time	Teeth: full set of 20 temporary Decreased need for naps
Intellectual and social	Follows a fast moving object Can respond to sounds Responds to his or her name Understands several words Can say mama, papa, and at least one or two other words Understands simple commands Tries to imitate animal sounds Connects names with objects Understands that objects continue to exist, even when they are not seen (object permanence) Points to objects with index finger Waves bye bye May develop an attachment to a toy or object Experiences separation anxiety and may cling to parents May make brief journeys away from parents to explore in familiar settings	Can use 10-15 words Says "no" (see holophrasis) Indicates when diaper is wet	Uses phrases composed of adjectives and nouns Begins to have temper tantrums Very ritualistic, has favorite toy or blanket Thumb sucking may be at peak	Vocabulary of about 350 words Obeys simple commands Helps undress self and put on simple clothes Shows sign of increased autonomy and individuality Does not share possessions—everything "mine" as in the "Toddler's Creed"	Begins to see self as separate individual; may still see other children as "objects"

It has long been known that markedly late achievement of developmental milestones is related to intellectual or physical disabilities. However, it was thought for a long time that within the general population no relationship between the age of passing developmental milestones and later intelligence is seen. It was only more recently discovered that early passing of developmental milestones indicates in general a higher level of intelligence. A study from 2007 based on more than 5,000 children born in the United Kingdom in 1946 showed that for every month earlier a child learned to stand, there was a gain of one half of one intelligence quotient point at age 8. Also a later 2018 study found a relationship between milestone achievement and intelligence in adulthood (in this case, the milestone used was being able to name objects/animals in pictures at less than 18 months, 18–24 months, and later than 24 months). The IQ of children who were able to form a sentence at less than 24 months of age averaged 107 points, whereas children who were able to form a sentence later than 24 months of age in young adulthood (20–34 years old) had an average IQ of 101. Early passing developmental milestones and the head circumference up to the age of 3 years explained about 6% of variance in IQ in adulthood. In comparison, parental socioeconomic status and the child's sex explained about 23% of the variance in IQ. However, experts advise against rushing children through milestones, as long as they are reaching them within a normal range.

1. Readiness: The Azrin and Foxx method of toilet training introduced the first set of objective criteria for determining whether a child is prepared to begin toilet training. The child should be physiologically and psychologically capable. Physiologic preparedness describes the ability of the child to perform tasks necessary for toilet training such as controlling their anal and urethral sphincter, sitting upright, and walking. Psychological readiness describes the child's motivation to become toilet trained and their ability to understand and follow directions.
2. Process training.
3. Parental response.

Young children squat instinctively as a continuous movement from standing up whenever they want to lower themselves to ground level. One- and two-year-olds can commonly be seen playing in a stable squatting position, with feet wide apart and bottom not quite touching the floor, although at first they need to hold on to something to stand up again.

Talking is the next milestone of which parents are typically aware. A toddler's first word often occurs around 12 months, but this is only an average. The child will then continue to steadily add to his or her vocabulary until around the age of 18 months when language increases rapidly. He or she may learn as many as 7–9 new words a day. Around this time, toddlers generally know about 50 words. At 21 months is when toddlers begin to incorporate two word phrases into their vocabulary, such as "I go", "mama give", and "baby play". Before going to sleep they often engage in a monologue called crib talk in which they practice conversational skills. At this age, children are becoming very proficient at conveying their wants and needs to their parents in a verbal fashion.