Abstract | In this paper, we present the results of an evaluation of preschool children playing five commercially available mobile computer games, the results of which will inform the user-led redesign of 'Space Vision', a serious mobile game for early identification and home-monitoring of vision problems for children of preschool age (3-5 years). Currently, Space Vision is a digitally gamified version of an established visual acuity testing method that uses a basic hidden-object-game mechanic. Initial testing revealed that the engagement and usability of Space Vision must be improved to maintain attention for repeated use. Though theories of human gameplay motivation provide the abstract components necessary to transpose this test into an immersive gameplay experience, they do not operationalise specific game design decisions for our target age group. To address this, we conducted a small-scale evaluation with 15 preschool children playtesting five successful children's games as the first step in our user-centred design process to inform the process of creating a more engaging and motivating prototype of Space Vision.