What is pediatric ADHD? Is it a psychiatric or neurological disorder? ADHD is a chronic neuropsychiatric disorder that is psychiatric in nature, but it is not yet possible to determine whether it is a neurological disorder. Does ADHD occur only in children? At what age does ADHD usually develop in children? ADHD usually develops in childhood and if left untreated can last a lifetime, resulting in adult ADHD, so it is not unique to children, but is a lifelong condition. The age limit for the onset of pediatric ADHD is unclear, but it must be before the age of 12. It is well documented that many children with ADHD have more fetal movements than others during fetal life.