In 1985, Thomas and French published results of a meta-analysis that examined sex differences in grip strength in children 5 years of age and older. Their analysis included results from only four studies, and no update has been published. The purpose of the current study was to use meta-analysis to examine sex differences in grip strength from birth to age 16. The analysis included 808 effects from 169 studies conducted in 45 countries between 1961 and 2023. The total sample was 353,676 (178,588 boys, 175,088 girls). From birth to 16 years of age, grip strength was consistently greater in boys than girls. Between 3 and 10 years old, the effect size was small-to-moderate, with female grip strength equaling 90% of male grip strength (Hedges g = 0.33-0.46). At age 11, the effect size decreased slightly, likely due to girls reaching puberty before boys (g = 0.29, 95% confidence intervals (CI) [0.22, 0.35]). At age 13, the effect size increased markedly likely due to male puberty (g = 0.63, 95% CIs [0.55, 0.70]). By age 16, the sex difference in grip strength was substantial, with female grip strength equaling 65% of male grip strength (g = 2.07, 95% CIs [1.86, 2.27]). Secondary analyses revealed that the sex difference in grip strength is broadly similar between countries and has been mostly stable since the 1960s, except for a narrowing of the difference among 5-10-year-olds after 2010. Various biological factors explain why, on average, boys are stronger than girls from birth onward.