A diagnosis of Autism spectrum disorder must be communicated gently to the diagnosed child in order to aid their self-awareness.
Reason
Often parents go through conflicting emotions once the doctor diagnoses their child and if there is no clear communication with the child, they may tend to absorb their negative emotions from their parents.
If this critical conversation does not take place, they make grow up confused and turn into adults with low self-esteem issues.
Time
As the child moves into different environments other than its home, he starts interacting with others and may start realizing that he or she is different than his peers or classmates. At this point when your child starts asking you questions like “why do I get so upset in a bright yellow room?”, calmly let him know that he has ASD.
Manner
Explain about Autism spectrum disorder in a very positive and non-judgmental tone. Emphasize the fact that every human being is unique in terms of behavioral, communicative and physical characteristics and it’s the differences that make us special.
We are curious to know how did you reveal the diagnosis to your child. Do share the reactions of your child with us.

References

Indiana University Bloomington. Indiana Resource Centre for Autism
Available at – https://www.iidc.indiana.edu/irca/learn-about-autism/getting-started-introducing-your-child-to-his-or-her-diagnosis-of-autism.html