All You Need to Know About Newborn, Infant, Baby and Toddler Age Ranges

The first few years of a child's life are filled with remarkable changes, significantly in their physical growth, cognitive development and social-emotional skills. These transformative years are broadly categorised stages: newborn, baby (or infant) and toddler. Often, these terms are used interchangeably, causing quite a bit of confusion, especially for new parents. This article will delve into the newborn, baby, infant and toddler stages, defining their age ranges, and outlining the typical developmental milestones associated with each. So, keep reading to find out the answer to questions such as, how many weeks is the newborn stage and when is a baby a toddler.

What Is the Age of a Newborn, Baby and Infant?

It's quite commonplace to hear different terms such as baby, newborn or infant when referring to your new arrival. Many parents are often puzzled, asking ‘how long is a baby a newborn?’ or ‘How long is the newborn stage?’ Although some of these terms can be used interchangeably, as there’s no set age range, some experts use ‘newborn’ for those under 3 months of age (12 weeks). So, a newborn age range can extend from birth to around 3 months of age, but what are the age ranges for infancy and when is a baby no longer a newborn? The terms baby or infant can also be used during the newborn stage, during pregnancy, and up until they’re about 1 year old. That means, your little one can be referred to as a baby or infant up until they’re 12 months old.

Child Developmental Stages: Newborn, Baby, Infant Age

Each child is distinctly individual and progresses at their own pace, but during your baby's initial year, you're likely to witness some significant strides in their growth and development. Here are some thrilling milestones you might observe by the time your little one celebrates their first birthday:

  • Their first smile

  • Your newborn’s vision becoming more focused and being able to see colours and objects in the distance

  • Reaching out for items

  • Starting to understand certain words, such as ‘no’, and recognising the names of people

  • Waving ‘bye-bye!’

  • Babbling or saying ‘mama’ or ‘dada’

  • Developing bonds and trust with loved ones and caretakers

  • Playing games, such as peekaboo

  • Crawling or pulling themselves up to stand

  • Walking along while holding onto furniture

  • Possibly taking their first steps

  • Developing fine motor skills, such as the pincer grasp, picking up small objects using their thumb and pointer finger.

As your little one grows and transitions from a little newborn into a more active baby, it’s natural to wonder if their development is on track. Every baby is unique and meets milestones at different rates, so don't hesitate to contact your baby's GP or health visitor if you have any questions or concerns about their development.




Throughout the first year of life, your baby is becoming more and more active. Now might be a good time to babyproof your home to keep your little one safe as they grow and explore.


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Toddler Age Range

It might seem as though you were just cradling your newborn yesterday, and suddenly, you're chasing after an active baby who just can't sit still! But when does a baby become a toddler? If you’re wondering how old a toddler is, the majority of experts agree that toddlerhood usually begins when your child is about 1 year old. This is the age where many babies are prepared to ‘toddle’ – ready to take those initial, slightly unsteady steps. The toddler age range runs from around 1 year (12 months) to around 3 years of age.

Child Developmental Stages: Toddler Age

This milestone is generally marked by significant strides in physical and cognitive abilities. Your once docile baby is now eager to explore the world, understand their surroundings, and assert their independence. It's a time of endless curiosity, frequent discovery, and yes, plenty of toddling! Here are some of the exciting and interesting developments your little one may make during toddlerhood:

  • Starting to walk and learning to walk alone and walk well

  • Beginning to run

  • Pulling their toys along behind them

  • Kicking a ball

  • Climbing

  • Feeding themselves

  • Imitating others’ behaviour

  • Developing an awareness of themselves and understanding ‘I’, ‘mine’ and ‘you’

  • Playing enthusiastically alongside other children

  • Engaging in pretend play and make-believe

  • Sorting by shape and colour

  • Saying four- and five-word sentences.

Every child develops and meets these milestones on their own timeline during their toddler years, so be prepared for your child to take more or less time than other children of the same age. If you have any concerns about your toddler’s developmental progress, such as their walking or language skills, contact their GP.



In Summary

A baby under about 3 months of age is often called a newborn; however, there’s no single or set definition. The term baby or infant may be used during pregnancy, after birth and up to around 1 year of age. Once your baby turns 1 year old, they are often referred to as a toddler. The toddler age range is usually from 1 year to 3 years of age.

Pre-school Age Range

Now that you have a rough idea of newborn, infant, baby and toddler age ranges, what comes after a toddler? Once your toddler is around 3 years old, they are often considered a pre-schooler or simply a child. The preschool age range may extend from 3 years up until they are around 5 years old. And they can be considered a child until they’re 12 years old – although, they may always seem like a child to you! How time flies!


A 4-year-old is neither a baby nor toddler. Usually, the term ‘toddler’ applies to children roughly between the ages of one and three. Thus, a 4-year-old is often referred to as a pre-schooler.

The Bottom Line

Despite the fact that your wee one might forever hold the title of ‘baby’ in your heart, there exists a variety of labels that characterise their growth and evolution. Typically, the term newborn is ascribed to infants under 3 months of age. Beyond this phase (and occasionally within it), your child may be categorised as a baby or an infant until approximately their first birthday.

But at what point does your tiny tot graduate to being a toddler? The consensus among experts is that the toddler stage commences around the age of 1. The toddler age range usually runs from 1 year to 3 years of age, and before you know it, your little one will be a pre-schooler! Each of these stages brings its own exciting developmental milestones and learning curves for your child. So, enjoy the journey!

How We Wrote This Article The information in this article is based on the expert advice found in trusted medical and government sources, such as the National Health Service (NHS). You can find a full list of sources used for this article below. The content on this page should not replace professional medical advice. Always consult medical professionals for full diagnosis and treatment.

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