Although autism is hard to diagnose before 24 months, symptoms often surface between 12 and 18 months. If signs are detected by 18 months of age, intensive treatment may help to rewire the brain and reverse the symptoms.

The earliest signs of autism involve the absence of typical behaviours—not the presence of atypical ones—so they can be tough to spot. In some cases, the earliest symptoms of autism are even misinterpreted as signs of a “good baby,” since the infant may seem quiet, independent, and undemanding. However, you can catch warning signs early if you know what to look for.

Some autistic infants don’t respond to cuddling, reach out to be picked up, or look at their mothers when fed.

Early signs

Your baby or toddler doesn’t:

• Make eye contact, such as looking at you when being fed or smiling when being smiled at.
• Respond to their name, or to the sound of a familiar voice.
• Follow objects visually or follow your gesture when you point things out.
• Point or wave goodbye or use other gestures to communicate.
• Make noises to get your attention.
• Initiate or respond to cuddling or reach out to be picked up.
• Imitate your movements and facial expressions.
• Play with other people or share interest and enjoyment.
• Notice or care if you hurt yourself or experience discomfort.

Developmental red flags

The following delays warrant an immediate evaluation by your child’s paediatrician:

By 6 months: No big smiles or other warm, joyful expressions.

By 9 months: No back-and-forth sharing of sounds, smiles, or other facial expressions.

By 12 months: Lack of response to name.

By 12 months: No babbling or “baby talk.”

By 12 months: No back-and-forth gestures, such as pointing, showing, reaching, or waving.

By 16 months: No spoken words.

By 24 months: No meaningful two-word phrases that don’t involve imitating or repeating.

Signs and symptoms in older children

As children get older, the red flags for autism become more diverse. There are many warning signs and symptoms, but they typically revolve around impaired social skills, speech and language difficulties, non-verbal communication difficulties, and inflexible behaviour.

Signs of social difficulties

• Appears disinterested or unaware of other people or what’s going on around them.
• Doesn’t know how to connect with others, play, or make friends.
• Prefers not to be touched, held, or cuddled.
• Doesn’t play “pretend” games, engage in group games, imitate others, or use toys in creative ways.
• Has trouble understanding feelings or talking about them.
• Doesn’t seem to hear when others talk to them.
• Doesn’t share interests or achievements with others (drawings, toys).

Basic social interaction can be difficult for children with autism spectrum disorder. Many kids on the autism spectrum seem to prefer to live in their own world, aloof and detached from others.

Signs of speech and language difficulties

• Speaks in an atypical tone of voice, or with an odd rhythm or pitch (e.g., ends every sentence as if asking a question).
• Repeats the same words or phrases over and over, often without communicative intent.
• Responds to a question by repeating it, rather than answering it.
• Uses language incorrectly (grammatical errors, wrong words) or refers to himself or herself in the third person.
• Has difficulty communicating needs or desires.
• Doesn’t understand simple directions, statements, or questions.
• Takes what is said too literally (misses’ undertones of humour, irony, and sarcasm).
• Children with autism spectrum disorder have difficulty with speech and language. Often, they start talking late.

Signs of non-verbal communication difficulties

• Avoids eye contact.
• Uses facial expressions that don’t match what they are saying.
• Doesn’t pick up on other people’s facial expressions, tone of voice, and gestures.
• Makes very few gestures (such as pointing). May come across as cold or “robot-like”.
• Reacts unusually to sights, smells, textures, and sounds. May be especially sensitive to loud noises. Can also be unresponsive to people entering/leaving, as well as efforts by others to attract the child’s attention.
• Atypical posture, clumsiness, or eccentric ways of moving (e.g., walking exclusively on tiptoe).

Children with autism spectrum disorder have trouble picking up on subtle non-verbal cues and using body language. This makes the “give-and-take” of social interaction very difficult.

Signs of inflexibility

• Follows a rigid routine (e.g., insists on taking a specific route to school).
• Has difficulty adapting to any changes in schedule or environment (e.g., throws a tantrum if the furniture is rearranged or bedtime is at a different time than usual).
• Unusual attachments to toys or strange objects such as keys, light switches, or rubber bands. Obsessively lines things up or arranges them in a certain order.
• Preoccupation with a narrow topic of interest, often involving numbers or symbols (e.g., memorising, and reciting facts about maps, bus schedules, or sports statistics).
• Spends long periods watching moving objects such as a ceiling fan or focusing on one specific part of an object such as the wheels of a toy car.
• Repeats the same actions or movements repeatedly, such as flapping hands, rocking, or twirling (known as self-stimulatory behaviour, or “stimming”). Some researchers and clinicians believe that these behaviours may soothe children with autism more than stimulate them.

Children with autism spectrum disorder are often restricted, inflexible, and even obsessive in their behaviours, activities, and interests.