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Signs of autism in children, from babies to teens

Autism looks different at different ages, and in different children. This is what parents and professionals tend to notice, what it does not mean on its own, and where to go next in Australia.

Updated 25 September 2026 · About 8 minutes to read · All guides

In short

  • Early signs of autism usually appear in the first one to two years, but some children are not recognised until school, the teenage years or adulthood.
  • In toddlers, many early signs are social: rarely pointing or showing, not consistently responding to their name, and rarely copying or playing pretend.
  • Autism can look different in girls, who may hide their differences by copying others, so it is often recognised later.
  • No single sign means a child is autistic, and many autistic children do not show the signs people expect.
  • If you are worried, start with your GP, child and family health nurse or paediatrician; support can start before a diagnosis.

What autism is, and what clinicians look for

Autism is a lifelong difference in how the brain develops and processes information. Clinicians look at two areas:

  • Social communication and interaction: back-and-forth conversation and sharing, non-verbal communication such as eye contact, gestures and facial expression, and making and keeping relationships.
  • Restricted and repetitive behaviours, interests and senses: repeated movements or speech, a strong need for sameness and routine, intense focused interests, and being over- or under-sensitive to sounds, textures, smells, lights or other sensations.

A diagnosis rests on a pattern: differences in all three parts of social communication, at least two of the four behaviour areas, signs from early development, and a real effect on daily life. The diagnostic manual notes that signs may not show fully until social demands outgrow a child's capacities, or may be masked by learned strategies later on.

Signs of autism by age

Most signs are about things a child does less often, or differently, rather than one dramatic behaviour. Some children have many early signs and others only a few, and signs can change or become clearer as children get older.

Babies (under 12 months)

Early signs usually appear in the first one to two years, but Healthdirect notes they may not be noticeable until 18 months or older. Early signs that can show up in babies include a baby who doesn't consistently smile back at familiar people, doesn't consistently respond to their name, or whose babble doesn't sound like a conversation with you. One of these on its own tells you little, and the Victorian surveillance research described below starts checking at around 12 months.

Toddlers (1 to 3 years)

This is when signs usually become clearer. A toddler might:

  • rarely point to things, or hold them up to show you
  • not consistently use eye contact to get your attention, or respond when called
  • not use gestures such as waving, and rarely copy what others do
  • show little interest in other children, and rarely start games like peekaboo or do pretend play
  • have trouble understanding simple one-step instructions
  • have intense interests in particular objects, repeat body movements, or use toys in unexpected ways
  • be easily upset by change, or be very sensitive to (or seek out) sounds, textures and other sensations

Victorian research shows these signs can be picked up early. In the Social Attention and Communication Study, more than 400 maternal and child health nurses were trained to check behaviours between 12 and 24 months, and around 38,000 children were monitored. Of the children the original tool flagged, 81% were later diagnosed autistic, and it was estimated to pick up 84% of autistic children. A free app based on this work, ASDetect, is designed for parents of children aged 11 to 30 months.

Preschool (3 to 5 years)

In young children, Healthdirect lists signs such as delayed speech or repeating certain words over and over, not pointing or showing you things, preferring to be alone, being very distressed by changes to routine, and repetitive movements such as hand-flapping, rocking or spinning.

School age

As social demands grow, differences can show more. Healthdirect lists trouble understanding body language and social cues, following instructions very literally, difficulty making friends, a narrow range of interests (such as only talking about certain topics), and sensory challenges.

A child can do well in class and still find everyday life hard. In a Western Australian study of 2,225 autistic children, those without intellectual disability had everyday adaptive skills well below what their IQ would suggest. Anxiety is common too: a study following 75 autistic children from 6 to 11 found changes in autism features went along with anxiety, ADHD and behaviour difficulties.

Teenagers

Raising Children Network lists signs such as not taking turns in conversation, talking a lot about intense interests but finding other topics hard, less eye contact or facial expression, preferring time alone, difficulty making friends, being upset by change, and sensory sensitivity or seeking. Teens who are aware of being different can feel alone, and anxiety and depression can come alongside autism.

Autism in girls

About three times as many males as females are diagnosed with autism, and many women are not diagnosed until adulthood. One reason is that autism can look different. Healthdirect notes that autistic girls and women are more likely to have stronger language and communication skills, a stronger ability to hide their differences by copying how others behave, and a tendency to keep negative emotions inside rather than show them.

The research is still developing. A US study following 183 autistic children from 3 to 11 found that girls' scores on a standard observation measure of autism features tended to fall over childhood, while boys' stayed stable. What that means is not settled. The Australian national guideline asks clinicians to take possible gender-based differences into account when considering a diagnosis.

No single sign means autism

Every sign on this page can turn up in children who are not autistic. Diagnosis rests on the overall pattern across both areas, present from early development and affecting daily life. The assessment also has to consider other explanations, such as intellectual disability or global developmental delay.

The reverse happens too. Many autistic children do not show the signs people expect. The manual describes the signs as ranges with examples, not a checklist every child must tick, and notes they can be masked by learned strategies. Healthdirect says autism is sometimes only noticed much later in life.

What to do next in Australia

  1. Talk to someone early. Raising Children Network recommends talking to your GP, child and family health nurse or paediatrician as soon as you can if you notice early signs. For a teenager, start with the GP.
  2. Know what an assessment involves. Under the national guideline, it includes a Comprehensive Needs Assessment (how your child is functioning, plus a medical evaluation) and, where appropriate, a Diagnostic Evaluation. For very young children, professionals may suggest watching for a while longer before deciding.
  3. Medicare. Children and young people under 25 can claim Medicare rebates on up to eight psychologist assessment sessions across their lifetime, once a paediatrician or psychiatrist has seen them and referred. There are still out-of-pocket costs.
  4. Support does not have to wait for a diagnosis. You can get supports and therapies while you wait for an assessment, and the national guideline says practitioners should refer to support as soon as a need is identified. From 1 October 2026, the government's Thriving Kids program starts for children aged 8 and under with developmental delay and/or autism with low to moderate support needs, and no diagnosis is needed. See our Thriving Kids guide.

If you are unsure whether an assessment is worth it yet, our free screener (choose "My child") suggests which assessment fits and tells you if one does not look like the right next step. It is not a diagnosis. You can read how a child autism assessment works.

Why earlier support helps, and what it can't promise

Australia's national guideline for supporting autistic children says supports during childhood can help children acquire skills, increase child and family wellbeing, reduce barriers around them and increase their participation in activities that matter to them. That is the case for acting early: help with communication, daily life and wellbeing while a child is growing, and a family that understands what is going on.

Support is not a cure, and it is not meant to be. The same guideline says supports should be neurodiversity-affirming and should not seek to "cure" autism, should be individualised to each child and family, and that practitioners should discuss the research evidence with families. Outcomes vary: in a US study of 125 autistic children followed from about 3 to 6, changes in measured autism severity had no clear relationship with intervention history. Be wary of any service that promises a particular result.

Questions people ask

What are the 3 main symptoms of autism?

There is no official list of three. Current criteria group autism into two areas: social communication and interaction, and restricted or repetitive behaviours, interests and sensory differences. The social communication area does have three parts, and all must be present: back-and-forth social and emotional exchange, non-verbal communication such as eye contact and gestures, and developing and keeping relationships.

What are the signs of autism in babies?

Early signs usually appear in the first one to two years, though they may not be noticeable until 18 months or later. In babies, parents sometimes notice less consistent smiling back, responding to their name, or babble that sounds like conversation. One sign on its own tells you little. If you are worried, raise it with your GP or child and family health nurse.

Is there an autism test for kids?

There is no single test. Autism is diagnosed through an assessment by qualified professionals, using standardised tools, questionnaires and observation alongside your child's developmental history. For toddlers aged 11 to 30 months, the free ASDetect app, based on Australian research, can help you decide whether to talk to a professional. Online screeners can point to a next step but cannot diagnose.

What is ASD in kids?

ASD stands for autism spectrum disorder, the formal diagnostic name for autism. It describes lifelong differences in social communication and in behaviour, interests and senses that start in early development and affect daily life. It is called a spectrum because children differ a lot in how it shows and how much support they need.

Can a child show signs of autism and not be autistic?

Yes. Most signs on their own also turn up in children who are not autistic, and signs can change or become clearer as children grow. An assessment looks at the overall pattern, how long it has been there and how much it affects daily life, and considers other explanations.

At what age can autism be diagnosed?

Autism can be reliably diagnosed by 24 months of age, though professionals may want to watch a very young child for longer before deciding. It is also sometimes only noticed much later, and many girls and women are not diagnosed until adulthood.

Wondering whether an assessment makes sense? The free screener takes about three minutes, for your child, your adult son or daughter, or yourself. It suggests which assessment fits, and it will tell you if one does not look like the right next step. Start the free screener.

Related

Child autism assessment · Thriving Kids and the NDIS changes · Autism levels · Stimming · Autism and ADHD assessment · All guides

Where this information comes from

We would rather you checked us than took our word for it. Every link below is the original source, not a summary of one.

Links to external sites are provided for reference. We do not control them and they may change. Last checked 25 September 2026.

This guide is general information, not medical advice. If you are worried about yourself or your child, talk to your GP.

Not sure where to start?

For your child, your adult son or daughter, or yourself. The free screener takes about three minutes and tells you which assessment fits — or whether you need one at all.

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