This cross-sectional study was conducted to investigate the influence of sleep habits, sleep problems, and lifestyle on sleep bruxism in Japanese elementary school children. In study 1, to confirm the reliability of replies provided by parents on children's sleep bruxism, we compared the scale of sleep bruxism frequency from questionnaires with actual sleep bruxism tooth wear in 49 elementary school children (22 males and 27 females). In study 2, a total of 1956 children (973 males, 983 females; mean age, 8.8 ± 1.8 years) and parents living in metropolitan Tokyo participated. Parents answered questionnaires on sleep habits, sleep problems, and lifestyle. Participants were classified as severe bruxism group (s-Bx) and non-severe bruxism group (ns-Bx) according to the frequency of sleep bruxism. The six grades were summarized into three categories: 1st/2nd grades (grades 1/2), 3rd/4th grades (grades 3/4), and 5th/6th grades (grades 5/6). The results suggest that the incidence of sleep bruxism in Japanese children living in Tokyo is strongly related to the disturbance of sleep habits and psychological stress, which can be caused by an owl-type lifestyle in children and parents.