We aimed to assess the test-retest reliability of five muscle strength and physical function tests in healthy children. Forty-one children (6–9 years) were tested three times 4–10 days apart. The test protocol included maximal isometric leg press, hand grip strength, squat jump, long jump, and a 30-sec sit-to-stand test (STST). When comparing test round 1 with 2 and 2 with 3, we found good-to-excellent retest reliability of leg press (intraclass correlation coefficient, ICC = 0.87 and ICC = 0.94), hand grip (ICC = 0.90 and ICC = 0.94), and long jump (ICC = 0.86 and ICC = 0.87). Initially, there was a moderate reliability of squat jump (ICC = 0.71), which was improved to ICC = 0.82 (round 2–3). Similarly, reliability of STST was improved from low (ICC = 0.63) to moderate reliability (ICC = 0.78). We conclude that leg press, hand grip, squat jump, and long jump tests are reliable measurements of children’s muscle strength and function, even without familiarization. Contrary, STST requires familiarization to ensure adequate reliability.