Functional constipation is a significant medical problem in pediatrics. Constipation often causes discomfort in children of any age and, in the absence of timely and effective treatment, can lead to chronic intoxication and the development of various complications, ultimately affecting the patient's quality of life. The article presents the definition of functional constipation in children over 4 years of age in accordance with the Rome IV Criteria (2016), etiology, pathophysiological mechanisms, clinic, diagnostic criteria and differential diagnosis of functional and organic constipation in preschool and school age children, possible complications. In accordance with the draft Consensus of the Society of Pediatric Gastroenterologists (2013), for a more objective assessment of the nature of the stool, the Bristol scale of stool forms is given. The physiology of the colon and the role of motor disorders in the occurrence of functional constipation are described. The physiology of the colon and the role of motor disorders in the occurrence of functional constipation are described. In accordance with the recommendations of the National School of Gastroenterology, the National Institute of Health and Clinical Excellence (NICE) in the UK, ESPGHAN and NASPGHAN, the basic principles of constipation therapy in preschool and school age children are given. The main groups of drugs that are used in the treatment of constipation in children of this age are described: stimulating and osmotic laxatives, prokinetics. Numerous foreign studies and clinical recommendations indicate that stimulants are effective and safe for the treatment of functional constipation, including in children's practice and are most in demand. The analysis of the use of one of the main drugs of the group of stimulating laxatives - sodium picosulfate in numerous international and Russian clinical studies is presented. The effectiveness and favorable safety profile of sodium picosulfate, the possibility of individual dose selection in connection with the liquid form of release are shown. A clinical example of the treatment of functional constipation in a 6-year-old child is given.