Sedentary past-times such as video gameplay are cited as having a negative effect on children's Fundamental Motor Skills (FMS) acquisition. Conversely, "exergames" utilise 3D sensor control systems (eg, Kinect®) to offer full body interactive user experiences in which FMS outputs are often part of the game "play" experience. This study evaluated the impact that participation in (1) commercial exergames and, (2) purpose-built exergames had on user locomotor skill outcomes (run, hop, skip, jump and slide) when both sets of games were deployed with a "principled" human-in-the-loop personalisation process. Typically developing children aged between 5 and 6 years were divided into two groups; a control group (n = 20; 45% girls) exposed to commercial exergames and, an experimental group (n = 20; 50% girls) exposed to purpose-built exergames. Gameplay was delivered daily, in the classroom, over a period of 8 weeks. The Test of Gross Motor Development-2 was utilised to assess children's locomotor skills at three time points (pre, interim and posttest). A mixed analysis of variance with repeated measures on time was conducted to evaluate results of the experimental group in comparison to the control group. A significant interaction effect was observed relating to Time × Group. Pairwise comparisons with a Bonferroni adjustment demonstrated that the experimental group made significant improvements for each locomotor skill (run, hop, skip, jump and slide) from pretest to posttest while the control group made significant improvements in only one locomotor skill (the slide) over the same timeframe. Results indicate that principled design and deployment of purpose-built exergames support high quality locomotor outputs and, improved outcomes over time.