Autism Spectrum Disorder (ASD) is a serious Neuro-Developmental Disorder that impairs a child's ability to communicate and interact with others. Autism significantly affects verbal and non-verbal communication and social interaction that adversely affects the child’s educational performance. It may also cause restricted repetitive behaviors, interests and activities.

The CDC latest statistics show that 1 in 59 children has Autism
(United States Centers for Disease Control & Prevention, 2018)

Autism Symptoms can vary from mild to severe
Autism can affect boys four times more than girls

No two children with Autism are the same, each one is different

Here are some common signs and symptoms that people with ASD might have:

• Little or No Eye-Contact
• Little or No Speech
• No Babbling by 12 months
• Not pointing at objects to show interest by 14 months
• Repeating words & phrases (Echolalia)
• Not responding to their own name by 12 months
• Stereotypic behavior: Flapping hands, rocking body, or spinning
• Not playing with peers
• No Play Pretend

• Sensory issues: Having unusual reactions to: sound, smell, taste, look, or feel
  Covering their ears when they hear loud noises
• Lining up toys or other objects
• Spinning the Wheels of a car
• Rocking Back and forth
• Preferring to have a familiar routine
• No sense of Danger

The Modified Checklist of Autism in Toddlers (M-CHAT) Revised Version is a list of informative questions about your child.
The answers can indicate whether the child should be further evaluated by a specialist such as a developmental pediatrician, neurologist, psychiatrist or psychologist.
You can take the M-CHAT-R/F Evaluation test for a toddler here.

1- Signs of ASD in pre-school children:

Spoken language

• delayed speech development (for example, speaking less than 50 different words by the age of two), or not speaking at all
• frequent repetition of set words and phrases
• speech that sounds very monotonous or flat
• preferring to communicate using single words, despite being able to speak in sentences

Responding to others

• not responding to their name being called, despite having normal hearing
• rejecting cuddles initiated by a parent or carer (although they may initiate cuddles themselves)
• reacting unusually negatively when asked to do something by someone else

Interacting with others

• not being aware of other people’s personal space, or being unusually intolerant of people entering their own personal space
• little interest in interacting with other people, including children of a similar age
• not enjoying situations that most children of their age like, such as birthday parties
• preferring to play alone, rather than asking others to play with them
• rarely using gestures or facial expressions when communicating
• avoiding eye contact

Behaviour

• having repetitive movements, such as flapping their hands, rocking back and forth, or flicking their fingers
• playing with toys in a repetitive and unimaginative way, such as lining blocks up in order of size or colour, rather than using them to build something
• preferring to have a familiar routine and getting very upset if there are changes to this routine
• having a strong like or dislike of certain foods based on the texture or colour of the food as much as the taste
• unusual sensory interests – for example, children with ASD may sniff toys, objects or people inappropriately 

2- Signs and symptoms of ASD in school-age children

Spoken language

• preferring to avoid using spoken language
• speech that sounds very monotonous or flat
• speaking in pre-learned phrases, rather than putting together individual words to form new sentences
• seeming to talk "at" people, rather than sharing a two-way conversation

Responding to others

• taking people’s speech literally and being unable to understand sarcasm, metaphors or figures of speech
• reacting unusually negatively when asked to do something by someone else

Interacting with others

• not being aware of other people’s personal space, or being unusually intolerant of people entering their own personal space
• little interest in interacting with other people, including children of a similar age, or having few close friends, despite attempts to form friendships
• not understanding how people normally interact socially, such as greeting people or wishing them farewell
• being unable to adapt the tone and content of their speech to different social situations – for example, speaking very formally at a party and then speaking to total strangers in a familiar way
• not enjoying situations and activities that most children of their age enjoy
• rarely using gestures or facial expressions when communicating
• avoiding eye contact

Behaviour

• repetitive movements, such as flapping their hands, rocking back and forth, or flicking their fingers
• playing in a repetitive and unimaginative way, often preferring to play with objects rather than people
• developing a highly specific interest in a particular subject or activity
• preferring to have a familiar routine and getting very upset if there are changes to their normal routine
• having a strong like or dislike of certain foods based on the texture or colour of the food as much as the taste
• unusual sensory interests – for example, children with ASD may sniff toys, objects or people inappropriately

Other conditions associated with ASD People with ASD often have symptoms or aspects of other conditions, such as: a learning disability
attention deficit hyperactivity disorder (ADHD)
epilepsy
dyspraxia
obsessive compulsive disorder (OCD)
generalised anxiety disorder
depression
bipolar disorder
sleep problems
sensory difficulties
Tourette's syndrome or other tic disorders

If your child has any of these problems, they may benefit from separate treatment, such as medication or cognitive behavioural therapy (CBT), in addition to their treatment for ASD.

information by: NHS UK

Typical infants are very interested in the world and people around them. By the first birthday, a typical toddler interacts with others by looking people in the eye, copying words and actions, and using simple gestures such as clapping and waving "bye bye". Typical toddlers also show interests in social games like peek-a-boo and pat-a-cake. But a young child with an ASD might have a very hard time learning to interact with other people.

Some people with an ASD might not be interested in other people at all. Others might want friends, but not understand how to develop friendships. Many children with an ASD have a very hard time learning to take turns and share—much more so than other children. This can make other children not want to play with them.

People with an ASD might have problems with showing or talking about their feelings. They might also have trouble understanding other people's feelings. Many people with an ASD are very sensitive to being touched and might not want to be held or cuddled. Self-stimulatory behaviors (e.g., flapping arms over and over) are common among people with an ASD. Anxiety and depression also affect some people with an ASD. All of these symptoms can make other social problems even harder to manage.

This information is from the CDC: Centers for Disease Control and Prevention.