Previous studies on brain functional connectivity networks in children have mainly focused on changes in function in specific brain re gions,as opposed to whole brain connectivity in healthy children.By analyzing the independent components of activation and network connectivity between brain regions,we examined brain activity status and development trends in children aged 3 and 5 years.These data could provide a reference for brain function rehabilitation in children with illness or abnormal function.We acquired functional magnetic resonance images from 15 3-year-old children and 15 5-year-old children under natural sleep conditions.The participants were recruited from five kindergartens in the Nanshan District of Shenzhen City,China.The parents of the participants signed an informed consent form with the premise that they had been fully informed regarding the experimental protocol.We used masked independent component analysis and BrainNet Viewer software to explore the independent components of the brain and correlation connections between brain regions.We identified seven independent components in the two groups of children,including the executive control network,the dorsal attention network,the default mode network,the left frontoparietal network,the right frontoparietal network,the salience network,and the motor network.In the default mode network,the posterior cingulate cortex,medial frontal gyrus,and inferior parietal lobule were activated in both 3-and 5-year-old children,supporting the three-brain region theory of the default mode network.In the frontoparietal network,the frontal and parietal gyri were activated in the two groups of children,and functional connectivity was strengthened in 5-year-olds compared with 3-year-olds,although the nodes and network connections were not yet mature.The high-correlation network connections in the default mode networks and dorsal attention networks had been significantly strengthened in 5-year-olds vs.3-year-olds.Further,the salience network in the 3-year-old children included an activated insula/inferior frontal gyrus-anterior cingulate cortex network circuit and an activated thalamus-parahippocampal-posterior cingulate cortex-subcortical regions network circuit.By the age of 5 years,nodes and high-correlation network connections (edges) were reduced in the salience network.Overall,activation of the dorsal attention network,default mode network,left frontoparietal network,and right frontoparietal network increased (the volume of activation increased,the signals strengthened,and the high-correlation connections increased and strengthened) in 5-year-olds compared with 3-year-olds,but activation in some brain nodes weakened or disappeared in the salience network,and the network connections (edges) were reduced.Between the ages of 3 and 5 years,we observed a tendency for function in some brain regions to be strengthened and for the generalization of activation to be reduced,indicating that specialization begins to develop at this time.The study protocol was approved by the local ethics committee of the Shenzhen Institute of Advanced Technology,Chinese Academy of Sciences in China with approval No.SIAT-IRB-131115-H0075 on November 15,2013.