A child is a toddler from age 1 through age 3. The American Academy of Pediatrics defines the toddler stage as 12 to 36 months, at which point a child transitions into the preschool stage (ages 3 to 5). The word “toddler” itself comes from “toddle,” meaning to walk unsteadily, which is exactly what kids this age are learning to do.
Why the Toddler Stage Starts at 12 Months
The first birthday isn’t an arbitrary cutoff. Around 12 months, most children are pulling themselves up to stand, walking while holding onto furniture, and may be taking two or three wobbly steps on their own. This shift from crawling to upright movement is the hallmark of toddlerhood and the reason the stage has its name. Before this point, a child is still classified as an infant.
Of course, not every child walks right at 12 months. Some start earlier, some later. The CDC revised its developmental milestone checklists in 2022 so that each milestone reflects the age by which at least 75% of children are expected to reach it. That change was designed to reduce the “wait and see” approach: if your child hasn’t hit a milestone placed at a given age, it’s worth bringing up with your pediatrician rather than assuming they’ll catch up.
What Happens During the Toddler Years
Two years is a long stretch in early childhood, and the difference between a 13-month-old and a 34-month-old is enormous. Here’s a rough sense of how the major areas of development unfold across this window.
Movement
Early toddlerhood is all about mastering walking. By around 18 months, most kids are walking without help and starting to climb. By their second birthday, many can run, kick a ball, and go up stairs with support. By the end of the toddler stage, close to age 3, most children can jump with both feet, pedal a tricycle, and navigate playground equipment with increasing confidence.
Language
Language growth during the toddler years is staggering. At 16 months, the median productive vocabulary for English-speaking toddlers is about 35 words. By 18 months it roughly doubles. Between 18 and 24 months, many children experience a “vocabulary explosion,” rapidly learning new words every day. By 30 months, that median vocabulary has grown well beyond what most parents can easily count. Research tracking nearly 5,000 toddlers found that stronger language skills during this period predict stronger language and cognitive abilities later in childhood.
Sleep
Toddlers between 12 and 24 months need 11 to 14 hours of sleep per day, including naps. Most toddlers transition from two naps to one somewhere between 12 and 18 months, and many still nap once a day through age 3. Sleep needs decrease only slightly as children move into the preschool years.
Nutrition
A toddler’s caloric needs are modest compared to older children. A two-year-old needs roughly 1,000 calories per day. The key nutrients to pay attention to are calcium (about 700 mg daily, roughly two cups of milk) and vitamin D (600 IU daily). This is also the stage when children shift from breast milk or formula as a primary food source to a full range of solid foods, and when picky eating often kicks in.
When a Toddler Becomes a Preschooler
The transition happens around the third birthday. There’s no single test a child passes to “graduate” from toddlerhood. Instead, the shift reflects a cluster of changes that typically come together around age 3: sentences become longer and more complex, imaginative play takes off, and children become more capable of following multi-step instructions and playing cooperatively with other kids. Many children also start a preschool or pre-K program around this time, which reinforces the social label.
In practical terms, if your child is between their first and third birthdays, they’re a toddler. If someone refers to a “young toddler,” they usually mean 12 to 18 months. An “older toddler” is typically in the 2 to 3 range. These aren’t official categories, but they’re useful shorthand because the developmental gap within the toddler years is so wide.