Autism is a developmental disorder, but unlike other developmental disorders, this condition is diagnosed based on behaviors and developmental milestones rather than on genetic or physiological markers.

Behavior rapidly grows and changes in babies and toddlers, so spotting the signs of autism at this young age can be complicated. Pediatricians generally start screening children for autism around 1 year old until about 3 years old.

Symptoms of autism may start showing up as early as 6 months old or as late as 4 years old. Most children are diagnosed around 2 years old, when autism symptoms begin to “stabilize.”

Autism & Early Childhood Diagnosis

Autism is a developmental disorder that is diagnosed based on differences in behavior, compared to neurotypical individuals. As the medical understanding of autism improves, changes to diagnostic criteria in manuals like the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) help doctors and counselors better recognize symptoms of autism and refer their clients for treatment.

While some people are not diagnosed until adolescence or adulthood, most people with autism are now diagnosed as children. The Centers for Disease Control and Prevention (CDC) reports that signs of autism most accurately show up by 2 years old. However, some children can be diagnosed as early as 18 months.

Clinicians report a range of diagnostic ages. Some children with mild or moderate symptoms in communication or socializing may not show signs of struggling until they are toddlers or older children.

Understanding Your Child’s Developmental Milestones

Medical professionals who work with children and research childhood development maintain a chart of developmental milestones. While each child will be a little different, reaching these benchmarks at different times, pediatricians can use this information to help parents understand that certain stages of development are normal, the age range when they will occur, and how to best support their child during these stages.

Parents may become concerned about their child if they don’t learn certain skills, like walking or speaking, at a certain point. They may be concerned if they see plateaus in learning. These may be normal parts of the child’s development, or they could signify a failure to hit developmental milestones. Regressions in learning or hitting a learning or skills plateau can indicate that the child has autism.

Some signs of autism may show up as early as 6 months old. For this developmental milestone, babies usually:

  • Recognize familiar faces and know if someone is unfamiliar.
  • Enjoy playing interactive games with others, especially parents and siblings.
  • Respond to other people’s emotions with their own facial expressions.
  • Enjoy looking at faces, including their own.
  • Begin making sounds and stringing some sounds together to try to form words.
  • Start to say consonants.
  • Make sounds other than crying to show joy or displeasure.
  • Show curiosity in their surroundings and others.

Between 12 and 24 months old, a toddler who is at risk for autism may show signs like:

  • Using unusual vocal tones or babbling with an unusual vocal register.
  • Unusual sensitivity to certain stimuli, especially sounds or textures.
  • Carrying objects around with them for a long time, but not playing with the item.
  • Unusual hand or body motions.
  • Lack of physical activity.
  • Playing with their toys alone and showing no interest in playing with parents or siblings.
  • Being difficult to soothe when upset.
  • Not recognizing faces or making eye contact.

These are crucial social, cognitive, and communicative developments. It is understandable for parents to worry if their child starts to take these steps and falters, or if the child does not pick these up at all. However, it is normal for symptoms like autism to emerge or fade starting around 6 months and continue to cycle for the next year or two. Autism symptoms become stable around 2 years old, which is when a diagnosis can be finalized.

Screening vs. Diagnosis for Autism

If you are concerned about your child’s progress, especially if there is a family history of autism, your pediatrician can help you understand your child’s development and then monitor for signs of autism. Monitoring for symptoms is different from diagnosing the disorder.

A 2019 study on early signs of autism surveyed 1,200 toddlers who had at least two developmental evaluations starting at 12 months (1 year) and 36 months (3 years). Among the group thought to have autism early on, less than 2% were ultimately found to be on the spectrum; however, among the toddlers who were not presumed to have autism, 24% ended up receiving an autism diagnosis. The study also found that, around the child’s first birthday, autism “stability” was about 50%. By 14 months, that accuracy went up to 80%.

Diagnosis Timeline

Your pediatrician may start monitoring your child for ongoing signs of autism if they begin to have developmental difficulties around 6 months or 1 year old. However, keeping track of these changes at your child’s regular checkups is screening, not a diagnosis.

Screening does not mean your child has autism or will have autism. If your pediatrician screens your child now for symptoms, once their developmental condition stabilizes, you can get evidence-based treatment for them if they are on the autism spectrum. Early intervention is crucial for your child’s development and long-term success in life.

Severe autism symptoms can sometimes be diagnosed as early as the child’s first birthday, but this is less common. If the child never makes eye contact, shows no interest in their surroundings, and does not make sounds, it is likely that they have a developmental disorder, which could be autism or another condition.

Work with your pediatrician to monitor your child’s progress and get appropriate behavioral therapy and other treatment as needed. This therapy is vital to helping your child manage their symptoms later in life.

On the other side, people who have mild autism symptoms may not get a diagnosis until they are teenagers or adults. They may have more subtle symptoms, like struggling to understand idioms or sarcasm. They may not make eye contact as children but will still socialize with others. They may communicate and learn at a high level, but rarely socialize with others.

While some people won’t get a needed diagnosis, these instances are becoming less common. As diagnostic criteria improve and more pediatricians routinely screen for autism, more children are being diagnosed and getting needed behavior therapy.

Early Diagnosis of Autism Helps Children & Their Families

Many parents may worry about their children’s development but feel unsure how to best support their child. If your child is monitored for autism and then diagnosed with the condition around 2 years old, you can begin working with an applied behavior analysis (ABA) therapist. This professional can help your child learn more words and form sentences, improve emotional regulation so they can manage behaviors, and otherwise support their development.

The earlier this therapy can start, the better for your child. Studies repeatedly show that early treatment results in better long-term outcomes for children with autism.

Nowadays, pediatricians are more likely to screen all their patients for autism. Several autism symptoms are subtle or variable, and parents may not notice them. These early screenings are crucial to ensuring cases of autism are recognized and officially diagnosed early, and interventions can then be accordingly delivered.

These screenings are also important for families, so they can understand their child’s unique condition and support the child’s development. Parents and siblings of children with autism can get support for themselves, so they can better support the child. All of this means better relationships, improved individual self-esteem, and a stronger family unit.

If you notice signs of autism in your baby or toddler, talk to your child’s pediatrician. In some cases, these signs may be part of your child’s normal developmental process, but in other cases, they may be signs of autism. With your pediatrician’s help, you can monitor these signs as your child grows.


Screening and Diagnosis of Autism Spectrum Disorder. (March 2020). Centers for Disease Control and Prevention (CDC).

CDC’s Developmental Milestones. (December 2019). Centers for Disease Control and Prevention (CDC).

Important Milestones: Your Baby by Six Months. (December 2019). Centers for Disease Control and Prevention (CDC).

22 Early Warning Signs of Autism. (March 2015). UC San Diego Health.

How Early Can Autism Be Diagnosed? (March 2013). Autism Speaks.

Evaluation of the Diagnostic Stability of the Early Autism Spectrum Disorder Phenotype in the General Population Starting at 12 Months. (April 2019). Journal of the American Medical Association (JAMA), Pediatrics.

Early Intervention for Autism. Eunice Kennedy Shriver National Institute of Child Health and Human Development.

Early Interventions, Explained. (October 2018). Spectrum.

Early Signs of Autism in Babies.

Hunting for Autism’s Earliest Clues. (April 2013). Autism Speaks.