Functional constipation (FC) is a common issue for children, often caused by low fiber intake or not drinking enough fluids. This study will look at how well a drug called linaclotide works for treating FC in young children, aged 6 months to just under 2 years. Linaclotide is a medicine that helps with constipation by increasing fluid in the intestines to make it easier to have a bowel movement. Children will either get this medicine or a placebo (a harmless pill that looks like the medicine but has no active ingredients) for 4 weeks. Parents will prepare the medicine at home and give it once a day. The study will take place at about 25 locations worldwide with about 30 children participating.

• Study lasts 4 weeks with regular clinic visits.
• Participants have a 50% chance of receiving placebo.
• Parents will prepare and give medicine daily.

Before joining, children must have certain symptoms like fewer than 3 bowel movements a week. They should not have other medical issues that could affect the study, like celiac disease or Down's syndrome. The study involves medical check-ups, blood tests, and keeping track of any side effects or changes in symptoms.