Inulin-type fructans have been used in infants and children because of their prebiotic potential to modulate the intestinal flora and influence the innate and adaptive immune response favorably. A mixture of long chain inulin (5-60 monomers) in combination with galactooligosaccharides (GOS) (2-7 monomers) has been added to infant formula in Europe in a 10-90% ratio for over 5 y. Clinical studies have demonstrated that these prebiotic formulas have significant effects on flora composition, improve stool consistency, decrease intestinal permeability, and reduce the incidence of gastrointestinal (GI) and respiratory infections and atopic dermatitis. Oligofructose in weaning foods consumed by toddlers increases fecal Bifidobacteria counts and decreases fecal Clostridia counts during consumption, leading to softer stools and fewer fever episodes and other GI symptoms. Synergy, a mixture of oligofructose and long chain inulin, is protective of the Bifidus flora during amoxicillin treatment. Few studies are available in adolescents. Calcium absorption is improved especially by Synergy. The same product, combined with Lactobacillus Rhamnosus and Acidophilus, induces significantly favorable effects on colonic ammonia (NH3) metabolism. The demonstrated bifidogenic effect of inulin and oligofructose on intestinal microbiota is probably not the only mechanism involved but may be the key to important immune mediated effects.