The goal of this clinical trial is to evaluate whether a probiotic supplement, BioKid LR®, can help maintain normal bowel movements after stopping laxative treatment (PEG 3350) in children aged 6 months to 17 years with functional constipation. The main questions it aims to answer are: Does taking BioKid LR reduce the chance of constipation coming back after stopping PEG? Can BioKid LR help children maintain regular bowel movements without needing to restart laxatives? Researchers will compare children who take BioKid LR with those who take a placebo (an inactive powder) to see if the probiotic helps prevent constipation from returning. Participants will: Take PEG 3350 (a common laxative) for 12 weeks along with either BioKid LR or a placebo. After 12 weeks, begin gradually stopping PEG while continuing with BioKid LR or placebo for another 12 weeks. Then continue only with BioKid LR or placebo for an additional 28 weeks (total study duration: 52 weeks). Keep a stool diary to track bowel habits and any side effects. Attend 5 study visits for physical exams and monitoring (weeks 0, 12, 24, 38, 52). The study includes 80 children and is double-blinded, meaning neither the doctors nor the participants know who is receiving the real probiotic or the placebo. The primary outcome is how long it takes for constipation to return after stopping PEG, requiring retreatment. Secondary outcomes include: How many children still need long-term treatment. How many have regular bowel movements without accidents (in children over 4 years old). Stool consistency and frequency. Children with certain medical conditions (like celiac disease or hypothyroidism) or who are taking medications that cause constipation cannot participate. This study is supported by Supherb Group, Israel, but they are not involved in designing or analyzing the research. The study has been approved by an ethics committee and follows international ethical guidelines.