A national survey has found a shocking increase in mental illness in children compared with just two years ago.

The Australian Psychological Society has found more than a quarter of psychologists say they’ve seen increasing numbers of preschool children with ADHD and other mental health issues.

Even 18-month-old children are being assessed for serious mental health issues.

The survey found there has been a 36 per cent increase in separation anxiety disorder, while cases of ADHD are up by 27 per cent.