Children are more susceptible to Giardia lamblia infection. Cells and hormones contained in human colostrum have an immunoprotective action against giardiasis, but the effects of advanced maternal age on these components are poorly understood. This study analyzed the colostrum of older women to determine melatonin and cortisol levels besides the participation of these hormones on the functional activity of phagocytes against G. lamblia. Colostrum samples were collected from younger (18 to 35 years old) and older (over 36 years old) lactating women. Colostrum samples were subjected to melatonin and cortisol determination, immunophenotyping, quantification of superoxide release, and assessment of phagocytic rate and microbicidal activity of phagocytes treated with hormones and in the presence of G. lamblia. Colostrum from mothers of advanced age contained higher melatonin and cortisol levels and a lower rate of cells expressing CD14 and CD15. In the colostru of these older mothers, melatonin increased superoxide release by phagocytes. In both groups, superoxide release by phagocytes treated with cortisol was higher in the presence of G. lamblia. In colostrum from mothers of advanced age, mononuclear (MN) phagocytes treated with melatonin showed higher phagocytosis of G. lamblia and higher microbicidal index. In younger mothers, MN and polymorphonuclear (PMN) colostrum phagocytes exhibited higher rates of G. lamblia elimination when treated with both melatonin and cortisol. In older mothers, cortisol and melatonin regulation for the functional activity of colostrum phagocytes against G. lamblia may represent an additional defense mechanism, relevant for the protection and treatment of parasitic infections in breastfed children.