Help & Support Bowel problems Causes of constipation For many children there is no underlying physical reason for what is causing their constipation. This is known as idiopathic constipation. Idiopathic constipation most commonly develops in children between 2 and 4 years old. There are, however, various possible causes of childhood idiopathic constipation: Withholding poo (also called ‘stool withholding’, which is when a child avoids emptying their bowels) Fear of the toilet (sometimes associated with pain or discomfort) Lack of a toilet routine (some children have such busy lives that it can be difficult to find time to sit and relax on the toilet each day) Resistance to potty training and an insistence that a nappy be put on to poo in An unbalanced diet Low fluid intake A change in routine Anxiety and emotional upset (for example when starting nursery or potty training) Some medications Constipation can be caused by some illnesses, for example cystic fibrosis or Hirschsprung’s disease. When an underlying illness has caused the constipation it is known as functional constipation. The following symptoms or signs could indicate that an underlying illness is the cause: Vomiting Weight loss or failure to gain weight A swollen, stretched tummy Severe pain A baby that does not pass its first stool (called meconium) within the first 48 hours of life Abnormalities of the anus Sores or ulcers near the anus Neurological problems (such as weak or paralysed legs) Excessive thirst Urinary symptoms Very pale-coloured poos Follow this link for information about spotting the signs of constipation.