The aim of this study is to examine young children`s language ability (vocabulary) based on their age and gender, and the socio-economic factors of family income and parent`s educational background. In addition, by examining the differences in the literacy environment at home due to family income, it explores the direction for the literacy environment provided at home and aims to find the direction for fully developing young children`s vocabulary. This research is targeted towards 1,624 children aged three, four and five, attending 19 kindergartens and 25 childcare centers (44 early childhood educational institutions in total) located in Seoul and metropolitan areas, as well as their 1,624 mothers. The findings of this research according to the research questions are as follows. The language ability (vocabulary) score varied depending on the young children`s gender, while female children were found to have significantly higher scores than males. Discrepancies were found in young children`s language ability (vocabulary) scores based on age. Young children`s language ability varied according to family income. Young children from high-income families scored higher than those from low-income families. Having examined the discrepancies by age, three, four, and five year olds from high-income families were shown to score higher. However, such a discrepancy showed the biggest gap at age three and there was a tendency for the gap to narrow at ages four and five.