The earliest signs of autism often show up between 12 and 24 months, though some children show differences as young as 6 to 9 months old. About 1 in 31 children in the United States are diagnosed with autism spectrum disorder, according to 2022 CDC surveillance data. If you’re noticing something about your child’s development that feels off, that instinct is worth paying attention to, and there are specific behaviors you can look for at every age.
Early Signs in Babies and Toddlers
Most parents first notice differences in how their child communicates and connects socially. In the first two years of life, these are the signs that often stand out:
- By 9 months: Not responding when you call their name. Not showing facial expressions like happiness, sadness, or surprise.
- By 12 months: Not playing simple back-and-forth games like pat-a-cake. Using few or no gestures, like waving goodbye.
- By 18 months: Not pointing at things to show you something interesting.
Limited or absent eye contact is another common early sign, and it can appear at any point in infancy. Some babies make eye contact early on and then gradually stop, while others rarely make it from the start. Keep in mind that no single behavior on its own means your child has autism. What matters is the overall pattern, especially when several of these signs show up together or persist over time.
Signs in Preschool and School-Age Children
Some children don’t raise concerns until they enter group settings like daycare, preschool, or kindergarten. That’s because the social demands at those ages are more complex, and differences become easier to spot. A child who seemed to be developing typically might start to struggle when they’re expected to have back-and-forth conversations, share imaginative play, or navigate friendships.
At this age, you might notice your child has trouble reading social cues, like not understanding when someone is joking or not picking up on another child’s emotions. They may take language very literally, have difficulty with changes in routine, or show intense, narrow interests that go well beyond what’s typical for their age. Some children repeat certain phrases, line up toys in precise ways, or get very distressed when small things change in their environment.
Repetitive Behaviors and Restricted Interests
Autism involves more than social and communication differences. To meet the diagnostic criteria, a child also needs to show at least two types of repetitive or restricted behaviors. These can look very different from one child to the next.
Some children repeat movements like hand-flapping, rocking, or spinning. Others develop rigid routines and become extremely upset if those routines are disrupted, even in minor ways. Many autistic children develop unusually focused interests, spending hours learning everything about a single topic like trains, weather patterns, or a specific video game. While all kids have favorite things, the intensity and narrowness of these interests is what sets them apart.
Sensory Differences
Many autistic children experience the world through senses that are dialed up too high or too low. Some are overwhelmed by things most people barely notice: the hum of fluorescent lights, the texture of certain clothing, or the noise level in a school cafeteria. They may gag on certain food textures, cover their ears at sudden sounds, or refuse to wear particular fabrics.
Other children are under-responsive to sensory input. They might not react to pain the way you’d expect, seek out intense physical sensations like crashing into furniture, or constantly touch objects around them. Some children experience both extremes, overreacting to some types of input while barely registering others.
Why Girls Are Often Missed
Autism is diagnosed far more often in boys, but that gap is partly due to how girls present. Girls tend to be better at “masking,” which means they consciously or unconsciously mimic the social behavior of the people around them. A girl might learn to make eye contact, copy her friends’ facial expressions, or rehearse conversation scripts, all of which can hide underlying difficulties.
Girls with autism also tend to have restricted interests that look more socially typical, like an intense focus on animals, celebrities, or fiction, which makes their behavior seem less unusual to adults. The result is that many girls aren’t identified until later in childhood or even adolescence, when the social demands of middle school and high school outpace their ability to mask.
Screening at the Pediatrician’s Office
Pediatricians typically screen for autism at the 18-month and 24-month well-child visits using a questionnaire called the M-CHAT-R. You’ll answer 20 yes-or-no questions about your child’s behavior, and the results fall into three categories. A score of 0 to 2 means low likelihood. A score of 3 to 7 means moderate likelihood, and the pediatrician will ask follow-up questions on the items that flagged. If two or more items still come back elevated after the follow-up, the screen is considered positive. A score of 8 to 20 means high likelihood, and the child should be referred for evaluation right away.
A positive screen does not mean your child has autism. It means a full evaluation is the next step. Similarly, a negative screen doesn’t rule autism out entirely, especially if your child is very young or if they mask well.
What a Full Evaluation Looks Like
A formal autism evaluation is more involved than a screening questionnaire. It typically includes direct observation of your child’s social and communication behavior, a detailed interview with you about your child’s developmental history, and sometimes cognitive or language testing. One widely used observation tool is the ADOS-2, where a clinician engages your child in structured activities designed to bring out social and communication behaviors. This is usually combined with a parent interview that covers your child’s early development and current behavior patterns.
No single test can diagnose autism on its own. The ADOS-2, for example, doesn’t capture repetitive behaviors well and doesn’t include developmental history, which is why clinicians combine multiple sources of information. Evaluations are conducted by developmental pediatricians, child psychologists, or multidisciplinary teams, and wait times can range from a few weeks to several months depending on your area.
The diagnostic criteria require persistent difficulties in three areas of social communication (like trouble with back-and-forth conversation, reduced sharing of emotions, and difficulty developing relationships) plus at least two types of restricted or repetitive behaviors. Symptoms need to have been present in early development, even if they weren’t recognized at the time.
You Don’t Need a Diagnosis to Get Help
If your child is under 3, you can request a free evaluation through your state’s early intervention program, which is funded under Part C of the Individuals with Disabilities Education Act. These programs are designed to identify and serve children with developmental delays as early as possible. The evaluation is multidisciplinary and includes an assessment of your family’s needs and priorities.
Here’s the important part: your child does not need a formal autism diagnosis to qualify. States define eligibility based on developmental delay, and each state sets its own threshold for what counts. If your child shows delays in communication, social skills, or behavior, they may qualify for services like speech therapy or developmental support regardless of whether the word “autism” appears on a report. You can find your state’s early intervention program by searching for “early intervention” plus your state name, or by asking your pediatrician for a referral.
For children 3 and older, your local school district is required to evaluate your child for free if you request it in writing. This is separate from a medical diagnosis and can open the door to school-based services and supports.