Consistent positive relationships have been found between birth weight and grip strength in adults but evidence in children is limited. In a prospective general population birth cohort (Southampton Women's Survey), grip strength and anthropometry (height and weight) were measured in 968 children at the age of 4 years. Mean (standard deviation (s.d.)) birth weight was 3.48 (0.52) kg. Birth weight, adjusted for sex and gestational age, was positively associated with grip strength (β = 0.22 kg/s.d. increase in adjusted birth weight; 95% CI 0.11, 0.34). The relationship was attenuated after adjustment for current height and weight such that it became non-significant (β = 0.03 kg/s.d. increase in adjusted birth weight; 95% CI−0.08, 0.14), suggesting that body size may be on the causal pathway. Early influences on muscle development appear to impact on grip strength in children, as well as adults.