Meeting the Australian 24-Hour Movement Guidelines for the Early Years is associated with better social-emotional development in preschool boys

24-hour Movement Guidelines for the Early Years promote that achieving all three-movement behaviour (sleep, sedentary behaviour and physical activity) recommendations is important for child health and development. We examined the association between meeting all, none and combinations of the Australian 24-Hour Movement Guidelines for the Early Years and social-emotional development in 1363 preschool (2–5 years) boys (52%) and girls. The PLAYCE study (Perth, Western Australia) parent survey collected data on children's social-emotional development (Strengths & Difficulties Questionnaire), screen time, sleep and socio-demographic factors. Physical activity was measured using seven-day accelerometry. Only 8% of preschoolers met all three guidelines (5% met none). A higher proportion of boys than girls met physical activity-related guideline combinations (physical activity only, physical activity plus screen, physical activity plus sleep, all), while more girls than boys met sleep only guidelines (all p < 0.05). In boys, meeting all guidelines, compared with none, was associated with a lower total difficulties score (adjusted difference in means −1.90; 95%CI: −3.88, −0.10). Meeting the screen only guideline or the screen plus sleep guidelines, compared with none, were associated with lower total difficulties, conduct problems and hyperactivity scores in boys (all p < 0.05). Meeting the physical activity plus sleep guidelines, compared with none, were associated with lower total difficulties and conduct problems scores in boys (all p < 0.05). No significant associations were found for girls. These findings highlight the positive impact for boys social-emotional development in meeting all guidelines. Future guideline development should consider dose–response evidence to identify guideline thresholds for specific health and developmental outcomes for boys and girls.