Maintaining a normal developmental trajectory of the gut microbiota is pivotal for child growth and health. A derailment of the development of the gut microbiota may trigger various temporary and enduring diseases and disorders. In the past two decades, increasing attention has been paid to the role of microorganisms in the microbiota-gut-brain axis. Through this axis and during sensitive periods such as infancy and puberty, the gut microbiota may hold more conspicuous relations to the gradually maturing host brain than at any other time point. In the research described in this thesis, we (1) described gut microbiota development in low-risk community children from birth to the age of 14 years, along with microbiota-related factors, and (2) explored relations between the gut microbiota and mental health in aspects of problem behavior, executive functions, prosociality, and social anxiety, in the same children.