A Study to Assess Adverse Events and Change in Symptoms With Linaclotide Versus Placebo in Pediatric Subjects, Ages 2 to 5 Years, With Functional Constipation

* Caregiver/parent/guardian/legally authorized representative (LAR) is willing and able to comply with procedures required in this protocol, prior to the initiation of any screening or study-specific procedures. In addition, the caregiver/parent/guardian/LAR who will be completing the electronic diary (eDiary) must be able to read and understand the assessments in the eDiary device and undergo training. * Participant meets modified Rome IV criteria for FC: For at least 1 month before Screening (Visit 1), the participant has had 2 or fewer defecations (with each defecation occurring in the absence of any laxative, suppository, or enema use during the preceding 24 hours) per week. In addition, at least once per week, participant must meet 1 or more of the following: * History of retentive posturing or excessive volitional stool retention. * History of painful or hard bowel movements (BMs). * Presence of a large fecal mass in the rectum. * History of large diameter stools. * At least 1 episode of fecal incontinence per week after the acquisition of toileting skills, if applicable.

* Participant history of: * Celiac disease, or positive serological test for celiac disease or the condition is suspected but has not been ruled out by endoscopic biopsy * Cystic fibrosis * Hypothyroidism that is untreated or treated with thyroid hormone at a dose that has not been stable for at least 3 months prior to Screening (Visit 1) * Down's syndrome or any other chromosomal disorder * Active anal fissure (i.e., participant reports having streaks of blood on the stool or on toilet paper and/or pain/crying with BM within 2 weeks prior to Screening). (Note: anal fissures that have resolved at least 2 weeks prior to screening would not be exclusionary.) However, if in the investigator's opinion, an anal fissure(s) may be the primary cause of participant's modified Rome IV FC criteria, the participant would not be eligible to participate in the study. * Anatomic malformations (e.g., imperforate anus, anal stenosis, anterior displaced anus) * Intestinal nerve or muscle disorders (e.g., Hirschprung disease, visceral myopathies, visceral neuropathies) * Neuropathic conditions (e.g., spinal cord abnormalities, neurofibromatosis, tethered cord, spinal cord trauma) * Lead toxicity, hypercalcemia * Inflammatory bowel disease * Childhood functional abdominal pain syndrome * Poorly treated or poorly controlled psychiatric disorders that might influence his or her ability to participate in the study * Lactose intolerance that is associated with symptoms which could confound the assessments in this study * History of cancer. (Note: participants with a history of cancer are allowed provided that the malignancy has been in a complete remission before Randomization (Visit 2). A complete remission is defined as the disappearance of all signs of cancer in response to treatment.) * Has conditions that could interfere with drug absorption including but not limited to short bowel syndrome.