The human intestinal tract harbors a diverse and complex microbial community, known as gut microbiota, which is critical in sustaining physiology, metabolism, nutrition and immune function. Dysbiosis of gut microbiota has been linked with obesity, hyperglycemia, hyperlipidemia, inflammatory bowel disease and other chronic inflammatory diseases. Gut microbiota is affected by host genetic markup, diet and life style; and therefore varied by human races and geographical locations. The development of gut microbiota starts before birth. The infant's microbiome can impact on human health in later life. The microbiome of pregnant women are associated with early-life microbiota of their offspring as well as growth, neurodevelopment and the development of allergic and neurocognitive disorders. Early childhood, when the microbiota is less mature and more malleable, is a golden age for microbiota manipulation to prevent disease. Studying microbiota at this golden age also allow us to dissect the development of a faulty microbiota and identify therapeutic targets to reverse it and cure diseases that are already developed.