At this time, what were once small developmental differences may start to become more evident as the child ages and their environment becomes more complicated.

Broadly speaking, the differences may be observed across social interactions and communication, and behaviour as well. Some common signs to be aware of include:

Social Interactions Signs

1. Limited eye contact: The child may avoid eye contact or have difficulty maintaining it.
2. Lack of response to name: Not responding to their name (but responding to other sounds). They may appear to be in their own world, disconnected from those around them.
3. Reduced shared interest: Rarely showing or sharing enjoyment, interests, or achievements with others. For instance, not bringing objects of interest, like toys or books, to show to a parent. The child may also seem quite happy to be left alone and pursue their own interests.
4. Difficulty understanding feelings: The child may struggle to understand other people's feelings and emotions. For instance, they may not understand to smile back when another person smiles at them.

Communication Signs

1. Delayed or disordered speech and language development: There may be limited speech according to language milestones, and a lack of gesture use and gesture understanding. “Speech delays” and language disorders on their own are not a sign of autism. A child with an isolated language disorder (who is not autistic) will point, gesture, or use facial expressions to make up for their lack of speech. A speech pathologist can conduct an assessment to identify the root cause of language challenges.
2. Repetitive language: There may be unusual speech patterns, such as repeating words and phrases (echolalia).
3. Difficulty with conversation: The child may have trouble starting or maintaining conversations. They may give unrelated answers to questions. There might also be a tendency to talk as a monologue and miss social cues, turn-taking and other communication conventions.

Behavioural Signs

1. Unusual or repetitive movements: Such as flapping, rocking, spinning, and waving their fingers in front of their eyes, or looking at things from unusual angles.
2. Strict routines: The child may experience stress at small changes in routines or environment and struggle with unexpected interruptions or new experiences.
3. Rigidity of thought:  The child may interpret words literally and have trouble understanding sarcasm or humour.
4. Focused interests: An intense interest in specific topics or objects is often present. They may be fixated on specific items such as doors or keys, and have little interest outside of these topics.
5. Unusual reactions to sensory input: The child may be over or under-reactive to sounds, smells, lights, textures, or tastes. An example of over-reactivity might be becoming distressed by busy or noisy public places such as shopping centres or sporting events. Under-reactive might mean they are under-sensitive to pain, heat or cold as an example. An occupational therapist can help better understand a child’s sensory preferences and processing. 
6. Unusual eating habits: Preferences for certain textures or avoiding specific foods is a common trait. Being a very fussy eater can have other causes, but it often occurs with autistic children.
7. Limited imitative play: An autistic child may have difficulty imitating actions or pretend play. Instead, they may prefer to line up toys or other objects, rather than playing with them in a ‘pretend’ way. They may choose to play with parts of toys instead of the whole toy, such as spinning the wheels of a toy truck over and over.
8. Lack of interest in peers or siblings: A child who regularly prefers to play alone rather than with other children (peers or siblings) may be showing signs of autism.

Some of the above signs can be present in children without autism and the presence of one or more of these behaviors does not necessarily mean a child is autistic. This list provides a range of behaviours that can indicate autism, or several other conditions. If you have concerns about your child's development, it's crucial to discuss your concerns with your GP or paediatrician.

The key reason behind encouraging parents and carers to observe and consider their child’s challenges, is that when an autistic child is diagnosed early, they can access support earlier. Early support means they are more likely to have better outcomes such as improved cognitive, developmental and adaptive functioning, enhanced language and social skills, and improved mental health compared to those who are diagnosed later. If autism is not diagnosed, then the early identification of other conditions or challenges can also benefit from intervention and give the child the best support to achieve their full potential.

Sources:

https://www.autismawareness.com.au/understanding-autism/signs-children

https://www.autismwhatnext.com.au/explore/children/road-to-diagnosis/knowing-the-signs

https://www.aspect.org.au/blog/early-signs-of-autism