There are abundant microbial communities in the human intestine, some of which have begun to colonize in it even before birth. The period from gestation to 2 years old is the window of opportunity for the development of the intestinal microbiota. During this period, its composition is susceptible to a variety of factors such as gestational age, delivery mode, feeding pattern, antibiotics, probiotics and prebiotics, environmental factors and host genes. The intestinal microbiota is crucial to infant development throughout its life and closely related to the health of infants. This review discusses the periods of colonization and change of the intestinal microbiota in early life and the factors affecting it, highlights the importance of the intestinal microbiota to infant growth and development, and puts forward the necessity of developing new foods.