The purpose of this study was to investigate the overall developmental characteristics of Korean children ages 0 to 8, and then explore specifically how children's social and emotional developmental levels are related to mothers' psychological states. This study was part of newly launched Boryung Baby Panel Study using web-based survey in 2011. The subjects were all mothers of 940 infants(0-2 years), 654 toddlers(3-5 years), and 484 school-age children(6-8 years) The mothers were asked to administer the web-based standardized developmental checklist for their child and fill out the questionnaires of psychological variables(life satisfaction, depression, parenting attitude, parenting efficacy, and parenting stress). The data was analyzed using descriptive analysis, t-test, and logistic regression for SPSS 20.0 windows. Major findings were as follows: 1. Infants(0 to 2) showed higher developmental level in cognition and fine motor skill domain compared to other domains. 2. Most toddlers(3 to 5) showed normal development in the most domain such as gross motor skill, fine motor skill, language, letter, number, self-help behavior. 3. In socio-emotional development domain, the ratio of risk or delay group were highest at both infant and toddler. 4. The 6-8 years old children that belong to risk group by the result of SDQ(emotion and behavior assessment) were also relatively high. 5. The relation of the children's socio-emotional developmental level and the mother's psychological variables were reciprocal. Based on these findings, the implications and the limitations of current study were discussed.