Personality trait measures for children are rarely based on the HEXACO Model of Personality, although research using this framework could provide important insights into the structure and development of children’s personalities. There is no HEXACO measure for elementary school children to date, and existing measures for older children seem inappropriate for this age group (e.g., due to some item content). We thus compiled two HEXACO-based short forms for measuring personality in elementary school children (8-10 years old) via parent reports. We applied a meta-heuristic item sampling algorithm (Ant Colony Optimization) in a training sample with 1,641 parent reports of 122 administered items. We selected a 54-Item Short Form comprising a latent facet structure and an 18-Item Ultra-Short Form comprising a correlated factors model for all six HEXACO dimensions but no facet structure. Both short forms showed good model fit in a holdout sample (n = 411) and sufficiently high re-test correlations after six months. Convergent and divergent validities for maximal performance measures and socio-emotional constructs (also measured six months after the initial personality assessment) were largely in line with theoretical assumptions. Overall, our study provides support for construct, re-test, and (predictive) criterion validity for the selected short forms.