The invention discloses a composition comprising a mixture of oligosaccharides, said mixture containing at least one N-acetylated oligosaccharide, at least one sialylated oligosaccharide and at least one neutral oligosaccharide, for use in the promotion magnesium absorption and/or magnesium retention. The composition preferably further comprises at least one long chain polyunsaturated fatty acid and/or at least one probiotic. This composition is particularly adapted for use in infants notably preterm infants.