In the present randomised double blind controlled study, the investigators will study the effects of oligosaccharides vs a placebo on the change in stool consistency and stool frequency in children with functional constipation.

Functional constipation (FC) in children is a common gastrointestinal (GI) disorder with a worldwide prevalence ranging from 0.7% to 29.6%. Complaints include infrequent bowel movement, painful defecation due to hard and/or large stools, fecal incontinence, and abdominal pain. Although the condition is rarely life-threatening, it strongly impairs quality of life. Oligosaccharides have been shown to relieve constipation symptoms in young adults and elderly. However, sufficient evidence is lacking linking oligosaccharides intake to improve symptoms in children with FC. The investigators hypothesize that oligosaccharides might be able to relieve symptoms of constipation in young children as well, among which softening stools.

In order to be eligible to participate in this study, a subject must meet all of the following criteria, as considered by a medical doctor:

• Written informed consent
• Aged 1-3 years
• Children that meet the Rome IV criteria for functional constipation

Exclusion Criteria:

A potential subject who meets any of the following criteria will be excluded from participation in this study:

• Children who suffer from any other GI complaints than functional constipation, known structural GI abnormalities, or previous GI surgery
• Any condition that would make it unsafe for the child to participate.
• Children with clinically significant cardiac, vascular, liver, pulmonary, psychiatric disorders, severe renal insufficiency, human immunodeficiency virus, acquired immunodeficiency syndrome, hepatitis B or C or known abnormalities of haematology, urinalysis, or blood biochemistry
• Children who are allergic to cow's milk or fish
• Use of antibiotics or other medicines or food supplements, and breast milk-feeding, 4 weeks prior to the study, except for the allowed escape medication
• Children that participate in another clinical trial