Physical activity is considered an effective method to improve sleep quality in adolescents and adults. However, there is mixed evidence among children. Our objectives were to investigate this association in children and to examine potential moderating variables. Eight databases were systematically searched, and we included all study designs with a sample of healthy children ages 3-13 years-old. We identified 47 studies for meta-analysis. Overall, we found little association between physical activity and sleep (r = 0.02, 95% confidence interval = −0.03 to 0.07). There was a high amount of heterogeneity in the overall model (I² = 93%). However, none of the examined variables significantly moderated the overall effect, including age, gender, risk of bias, study quality, measurement methodology, study direction, and publication year. Exploratory analyses showed some weak, but statistically significant associations for vigorous physical activity with sleep (r = 0.09, 95% CI = 0.01 to 0.17, I² = 66.3%), specifically sleep duration (r = 0.07, 95% CI = 0.00 to 0.14, I² = 41.1%). High heterogeneity and the lack of experimental research suggest our findings should be interpreted with caution. The current evidence, however, shows little support for an association between physical activity and sleep in children.