DOCS TRY TO DIAGNOSE AUTISM, OTHER MENTAL ISSUES IN BABIES
Within days of their birth, healthy babies will look you in the eye. By 4 months, they will delight in others. And by 9 months, they will exchange smiles.
Ref. https://www.cnn.com/2007/HEALTH/05/23/baby....y.ap/index.html
Averages is the best way to see. How does your child behave as compared to others? With my child the first thing I noticed was his lack of awareness. Whereas children in the same age group would figure certain things out or play specific games my child would not have a clue what was going on. Speech also tells a lot - how much a child says and the way he/she uses words, etc.