Children change their body size, shape, and gross motor coordination (GMC) as they grow. Further,GMCis expected to link to changes in children's body size, physical activity (PA), and physical fitness (PF). The objective was to modelGMCchanges in children followed longitudinally and to investigate associations between these changes andPAandPFlevels. A total of 245 children (122 girls) were observed at 6 years of age and followed annually until 9 years. A sequence of allometric models was fitted, that is, 1. body mass, stature, andPA; 2. addition of fourPFtests; 3. addition of four morePFtests. In Model 1, changes inGMCare nonlinear, and body mass (−0.60 ± 0.07,P < .001) and stature (2.91 ± 0.35,P < .001) parameter estimates were significant suggesting children with a more linear body size/shape showed higherGMCperformances. Girls tend to outperform boys across time, andPAwas not associated withGMCchanges. Model 2 fitted the data better, and thePFtests (handgrip, standing long jump, 50‐yard dash, and shuttle run) were significantly linked toGMCchange. In Model 3, adding the remainingPFtests did not change the order of any factors importance. The greatestGMCchanges were achieved by children whose body size/shape has an ectomorphic dominance across the years. Considering that leaner and physically fitter children tended to be more coordinated, physical education should also focus onPFdevelopment in components related to muscular strength, speed, agility, and aerobic capacity, along with nutritional education to reduce fat mass.