This study examines how working parents’ work attitudes (i.e., workaholism and work engagement) are associated with their child’s psychological well-being. Based on the Spillover-Crossover model (SCM), we hypothesize that (a) work-to-family spillover (i.e., work-to-family conflict and facilitation) and (b) employee happiness will sequentially mediate the relationship between parents’ work attitudes and their child’s emotional and behavioral problems. A cross-sectional survey was conducted among Japanese dual-earner couples with pre-school child(ren). On the basis of valid data from 208 families, the hypothesized model was tested using structural equation modeling. For both fathers and mothers simultaneously, workaholism was positively related to work-to-family conflict, which, in turn, was negatively related to happiness. In contrast, work engagement was positively related to work-to-family facilitation, which, in turn, was positively related to happiness. Fathers’ and mothers’ happiness, in turn, were negatively related to their child’s emotional and behavioral problems. Results suggest that parents’ workaholism and work engagement are related to their child’s emotional and behavioral problems in opposite ways, whereby parents’ spillover and happiness mediate this relationship. These findings support the SCM and suggest that decreasing workaholism and improving work engagement may not only improve employees’ happiness, but also decrease their child’s emotional and behavioral problems.