A popular activity among young children is the use of mobile devices and apps. Yet, the impact of mobile devices on learning and development is rather underexplored. The limited studies identified explore effects on literacy development and communication and report on mixed findings. A considerable gap is observed as to how the use of mobile apps relates to young children's understanding in diverse domains including science learning, and to extend, whether and how mobile apps should be used and how in early years' settings. The aim of this paper is to shed light on this area by examining the learning effects of touch screen mobile game applications, in particular the game Angry Birds, on two groups of preschoolers 4 and 5 years old respectively. Evidence from a comparative study with 32 participants reveal significant differences between the two groups in terms of game skills and their understanding of projectile motion. Implications for educational stakeholders, parents and app designers are discussed along with future research directions.