The purpose of this research is to identify relationship among parent attachment and peer relationship and happiness of children. Afterwards, it looks into how peer relationship mediates parent attachment and influences happiness of children. For this research a survey on parent attachment, peer relationship, and happiness was done with total 272 elementary students living in D district of Daegu city. The collected data was statically processed by using SPSS WIN 20.0 program by frequency analysis, descriptive statistics, and multi regression analysis. The result of this research as follows. First, children’s happiness appears to be affected by peer relationship and parent attachment. Second, in relationship between happiness of children and parent attachment, appeared to be partially mediating. This research conclusion implies that peer relationship should be considered first in terms of happiness of children. That is, children can be happy when they have positive peer relationship. As this is the case, to promote their happiness increase of absolute time and opportunities for forming positive peer relationship and support programs such as making peer relationship are required. Furthermore, it was found out that parent attachment affects not only happiness of children but also peer relationship, thus, various methods to form parent attachment for their happiness are needed.