Objective: We sought to study and procure reference values for weight-related maximum isometric grip force (MIGF), maximum voluntary force in relation to body weight (Fmvrel) and peak whole body stiffness (pKwb) in multiple one-legged hopping (m1LH) in childhood. Methods: We examined 868 children and adolescents (436 female) aged 3 to 19 yrs. Weight-related results are reported as multiples of earth’s gravity (g). Results: MIFG and Fmvrel_m1LH are highly linearly correlated with body weight. After adjustment for weight, mean Fmvrel_m1LH increases from the age of 3 to 6 yrs, then remains at 3.33 g (SD 0.31 g) between 6 and 19 yrs, independent of age and gender. The difference between legs decreases from 10% at 3 yrs to a constant 5.5% after the age of 7 yrs. Weight-adjusted MIGF also increases steeply from 3 to 6 yrs, then shows a further linear, less steep increase—in males through to age 19 yrs while females show a near-standstill after the age of 12 yrs. pKwb_m1LH increases from the age of 7 yrs. Conclusion: This data from normal children from a healthy Caucasian population provide a reference for tests of motor function.