The first 1000 days of life is a unique period when foundations for optimum health and development across the lifespan are established. GI tract and immune system immature at birth whereas colonization with microbes begins right after birth. 

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Probiotics are especially well-suited for children and infants, since they can aid in the development of a normal microbiota in infants, or help in modulating the microbiota and the immune system in cases of microbial imbalance.