The aim of this study is to examine the relationship between toddlers' and pre-schoolers' sleep problems, screen-based media use, sleep regimen and the role of child emotional reactivity in this relationship. This research is a part of an extensive national study. Participants are 754 children aged 2-5 years old, and their parents. Sleep problems were related to emotional reactivity and sleep regimen. The longer screen time was associated with the higher levels of emotional reactivity, but not with sleep problems; however, emotional reactivity was significant for more sleep problems, inconsistent sleep regimen and longer screen time. Results of paths analysis have revealed that emotional reactivity both directly and through the mediators -- sleep regimen, screen time and a screen-based device positioned in a child's bedroom -- significantly predicted sleep problems. Emotional reactivity plays a considerable role as a risk factor when examining the effect of screen media use for sleep problems.