The goal of this observational study is to compare the brain functional network between children with autism and typical development, using magnetic resonance imaging (MRI), electroencephalogram/event-related potentials(EEG/ERPs) and functional Near Infrared Spectrum(fNIRs). The main questions it aims to answer are as follows: 1. What are the differences of the functional brain network between autism and TD children? 2. What are the differences of the brain activity in response to special social stimulus between autism and TD children? Participants will receive developmental/intelligence assessments (Griffiths Mental Developmental Scales/Wechsler Preschool and Primary Scale of Intelligence-IV/Wechsler Intelligence Scale for Children-IV for children of different ages), social assessments(Autism Diagnostic Observation Schedule-2nd Edition/Social Communication Questionnaire), EEG/ERPs and fNIRs in resting and task states, and head MRI in natural sleeping state(without sedative).

The cross-sectional observational study will be performed to compare the differences of functional brain network and reactions to social stimulus between children with autism and typical development. The investigators will recruit children aged between 2 to 17 years and 11 months old. They need to receive the mentioned assessments and medical examinations for at least once.

Case group:

Inclusion Criteria:

1. Children diagnosed with ASD according to a clinical judgement based on the criteria of ASD in DSM-5 and further confirmed with ADOS-2;
2. Ages 2-17 years;
3. Parents/caregivers understand the content of the study and agree to participate in.

Exclusion Criteria:

1. Rett Syndrome, Fragile X Syndrome, Angelman Syndrome, Prader-Willi Syndrome, tuberous sclerosis, and other syndromes caused by known genetic defects or inherited metabolic diseases;
2. Children with brain injuries, specific chronic or congenital diseases.
3. The gestational age is less than 37 weeks, or the birth weight is lower than 2500g.
4. Children cannot receive the head MRI examination.

Control group:

Inclusion Criteria:

1. Healthy children age between 2 to 17 years.
2. Children without the family history of ASD or other neurodevelopmental/mental diseases.
3. Parents/caregivers understand the content of the study and agree to participate in.

Exclusion Criteria:

1. Children with brain injuries, specific chronic or congenital diseases.
2. The gestational age is less than 37 weeks, or the birth weight is lower than 2500g.
3. Children cannot receive the head MRI examination.

The observation study will be performed in children with ASD and healthy, typically developing children.