constipation​in children is due to many causes mainly hypothyroidism, intestinal pseudo obstruction,hisprung disease. these are following causing constipation in children from birth NONORGANIC (FUNCTIONAL)—RETENTIVE ANATOMIC Anal stenosis, atresia with fistula Imperforate anus Anteriorly displaced anus Intestinal stricture (postnecrotizing enterocolitis) Anal stricture ABNORMAL MUSCULATURE Prune-belly syndrome Gastroschisis Down syndrome Muscular dystrophy INTESTINAL NERVE OR MUSCLE ABNORMALITIES Hirschsprung disease Pseudoobstruction (visceral myopathy or neuropathy) Intestinal neuronal dysplasia Spinal cord defects Tethered cord Spinal cord trauma Spina bifida DRUGS Anticholinergics Narcotics Methylphenidate Phenytoin Antidepressants Chemotherapeutic agents (vincristine) Pancreatic enzymes (fibrosing colonopathy) Lead Vitamin D intoxication METABOLIC DISORDERS Hypokalemia Hypercalcemia Hypothyroidism Diabetes mellitus, diabetes insipidus INTESTINAL DISORDERS Celiac disease Cow’s milk protein intolerance Cystic fibrosis (meconium ileus equivalent) Inflammatory bowel disease (stricture) Tumor Connective tissue disorders Systemic lupus erythematosus Scleroderma PSYCHIATRIC DIAGNOSIS Anorexia nervosa get evaluated from your pediatrician