Autism can sometimes be diagnosed from around 18 months of age, although many children are diagnosed later. Research shows that signs of autism may be present during infancy, and reliable autism assessments can often be completed from around the age of two years. The earlier a child’s needs are recognised, the sooner they can access understanding, support and appropriate adjustments.
In this article, I explain what age autism can be diagnosed, the earliest signs of autism, how autism is assessed in young children, and why early identification can be beneficial.
At What Age Can Autism Be Diagnosed?
Many parents are surprised to learn that autism can sometimes be diagnosed as early as 18 months of age. Research suggests that experienced clinicians can identify autism reliably in some toddlers from this age, particularly when clear social communication differences and repetitive behaviours are present (Zwaigenbaum et al., 2015).
However, most autism assessment services assess children from around two years of age onwards, as developmental patterns become clearer and diagnostic accuracy increases.
It is important to remember that autism presents differently in every child. Some children show obvious signs during infancy, whilst others develop skills typically during their early years and differences only become apparent later during nursery or school.
Therefore, there is no single age at which autism is diagnosed. The best age for assessment is when concerns arise, regardless of the child’s age.
Can Autism Be Diagnosed Before the Age of Two?
Yes. In some cases, children can receive an autism diagnosis before their second birthday.
Studies have found that developmental differences associated with autism can be detected within the first year of life, particularly in children who have an older autistic sibling and are considered at higher likelihood of being autistic themselves (Jones et al., 2014).
Nevertheless, diagnosing autism in very young children can be challenging because all children develop at different rates. A comprehensive assessment considers not only current behaviours but also developmental history, communication skills, play, social interaction and sensory differences.
For some children, clinicians may monitor development over time before confirming a diagnosis.
When Do the Earliest Signs of Autism Appear?
Research suggests that early indicators of autism may emerge between 6 and 12 months of age, although the timing varies significantly between children.
Some parents report that they noticed differences from infancy, whereas others only begin to notice signs when expectations around language, social interaction and play increase during toddlerhood.
It is important to understand that the presence of one sign alone does not necessarily indicate autism. Clinicians consider the overall pattern of development rather than individual behaviours in isolation.
Early Signs of Autism in Babies
Possible early signs of autism in babies may include:
- Reduced eye contact
- Limited social smiling
- Reduced interest in faces
- Less frequent sharing of enjoyment with others
- Limited response to their name
- Differences in babbling or early communication
- Repetitive movements of the hands, fingers or body
- Unusual responses to sensory experiences such as sounds, textures or movement
Some babies may be highly observant and content to play independently, while others may appear unusually sensitive to everyday sensory experiences.
Early Signs of Autism in Toddlers
Parents are often searching online for signs of autism in toddlers when concerns first arise. Common indicators may include:
Communication Differences
- Delayed speech and language development
- Limited use of gestures such as pointing
- Difficulty following another person’s point or gaze
- Reduced sharing of interests with others
- Not consistently responding to their name
Social Interaction Differences
- Limited interest in interacting with peers
- Preferring solitary play
- Difficulty engaging in turn-taking activities
- Limited use of eye contact during interaction
Play Differences
- Repetitive use of toys
- Lining up objects
- Strong preference for particular toys or activities
- Limited imaginative or pretend play
Repetitive Behaviours and Interests
- Hand flapping
- Repetitive body movements
- Repeating words or phrases
- Strong preference for routines
Sensory Differences
- Sensitivity to sounds, textures, smells or lights
- Strong reactions to everyday sensory experiences
- Sensory-seeking behaviours such as:
- Sniffing objects
- Licking items
- Chewing non-food items
- Seeking movement or pressure
Research shows that sensory differences are extremely common in autistic children and form part of the diagnostic criteria recognised by the DSM-5-TR (American Psychiatric Association, 2022).
What Should I Do if I Think My Child Has Autism?
If you are concerned about your child’s development, trust your instincts.
You can discuss your concerns with:
- Your health visitor
- Your GP
- Your child’s nursery or preschool
Many parents find it helpful to write down examples of behaviours they have noticed before attending appointments.
A healthcare professional may use a screening questionnaire such as the Modified Checklist for Autism in Toddlers (M-CHAT-R). Screening tools cannot diagnose autism, but they can help determine whether a full autism assessment is appropriate.
If concerns remain, your child should be referred for a comprehensive autism assessment.
How Is Autism Diagnosed in Young Children?
A high-quality autism assessment usually involves:
- Detailed developmental history from parents
- Observation of the child’s communication and interaction
- Structured assessment tools
- Consideration of sensory differences
- Information from nursery or educational settings
- Input from appropriately trained clinicians
NICE guidance recommends that autism assessments should be completed by multidisciplinary professionals with expertise in autism and child development (NICE, 2021).
Following assessment, parents receive a detailed report outlining the child’s strengths, differences and support needs, regardless of whether diagnostic criteria are met.
Why Are Some Children Diagnosed Later?
Although autism can be diagnosed early, many children wait years for an assessment. Many parents are told to ‘watch and wait’ from professionals who believe difficulties are due to a language delay or global developmental delay.
Across England and Wales, significant delays continue to affect autism assessment services, with some families waiting several years between referral and diagnosis. This means that a child’s age at diagnosis is often influenced by local service availability rather than when signs first became apparent.
Some children are also diagnosed later because:
- Their characteristics are more subtle
- They have strong language skills
- They develop coping strategies
- Their needs only become apparent when social demands increase
Is an Autism Diagnosis a Label?
Some parents worry that seeking an autism assessment might result in their child being “labelled”.
In reality, an autism diagnosis is not about labelling a child. It is about understanding how they experience the world.
A diagnosis can help explain a child’s differences and provide a framework for understanding their strengths, challenges and support needs. For many families, receiving a diagnosis brings relief, clarity and validation after months or years of uncertainty.
What Are the Benefits of an Early Autism Diagnosis?
Research suggests that early identification can help children access appropriate support during critical periods of development.
Potential benefits include:
- Better understanding of a child’s communication style
- Access to specialist support and advice
- More effective educational planning
- Appropriate adjustments in nursery and school
- Improved family understanding
- Access to local support groups and services
- Evidence to support applications for benefits or educational provision where appropriate
Perhaps most importantly, a diagnosis can help a child grow up understanding that their differences are valid and recognised.
When Is the Best Time to Get a Child Assessed for Autism?
Parents often ask, “Should I wait and see?”
Whilst every situation is different, most experts agree that if concerns are significant enough for you to be wondering about autism, it is worth seeking advice.
You do not need to wait until school age.
The best time to seek an autism assessment is when concerns first arise. Early assessment does not force a diagnosis, but it can provide reassurance, guidance and a better understanding of your child’s development.
What Should I Do Next?
If you’re asking yourself “How early can autism be diagnosed?”, you have already taken an important first step by seeking information.
Whether you choose an NHS pathway or a private assessment, obtaining professional advice can help you understand your child’s development and decide what support, if any, might be helpful.
At Jo Condon Autism Assessments, we offer autism screening and comprehensive autism assessments for children, helping families gain clarity and access support without lengthy waiting times.
If you would like advice about whether an autism assessment may be appropriate for your child, contact our team and we will be happy to discuss your concerns.
References
American Psychiatric Association (2022) Diagnostic and Statistical Manual of Mental Disorders: DSM-5-TR. 5th edn. Washington, DC: American Psychiatric Publishing.
Jones, W., Klin, A., Venet, C., Johnson, M.H. and Chawarska, K. (2014) ‘Attention to eyes is present but in decline in 2-6-month-old infants later diagnosed with autism’, Nature, 504(7480), pp. 427-431.
National Institute for Health and Care Excellence (NICE) (2021) Autism spectrum disorder in under 19s: recognition, referral and diagnosis (CG128). London: NICE.
Zwaigenbaum, L., Bauman, M.L., Choueiri, R., Kasari, C., Carter, A., Granpeesheh, D. and others (2015) ‘Early identification and interventions for autism spectrum disorder: executive summary’, Pediatrics, 136(Supplement 1), pp. S1-S9.
