Participants aged 10-18 years will be randomly assigned to receive either PEG 60 ml/kg/day or PEG 30 ml/kg/day plus oral bisacodyl 10-15 mg/day or sennosides 2mg/kg/day for 2 days prior to the colonoscopy. The outcome measures will be:bowel cleansing efficacy, scored by a blinded endoscopist using the Ottawa scale and Aronchick Scale (the mean total score, proportions of participants with excellent/good and with poor/inadequate bowel preparation), and the patient satisfaction score(0-10)with the method of preparation for the colonoscopy evaluated with the visual analog scale. Analysis will be done on an intention to treat basis.