In this paper, we present an educational game for an iPhone and a Tablet PC. The main objective of the game was to reinforce children's knowledge about the water cycle. The game included different interaction forms like the touch screen and the accelerometer and combined AR mini-games with non-AR mini-games for better gameplay immersion. The main differences between the two devices were screen size and weight. A comparative study to check how these differences affect different aspects was carried out. Seventy-nine children from 8 to 10 years old participated in the study. From the results, we observed that the different characteristics (screen size and weight) of the devices did not influence the children's acquired knowledge, engagement, satisfaction, ease of use, or AR experience. There was only a statistically significant difference for the global score in which the iPhone was scored higher. We would like to highlight that the scores for the two devices and for all the questions were very high with means of over 4 (on a scale from 1 to 5). These positive results suggest that games of this kind could be appropriate educational games and that the mobile device used may not be a decisive factor. (Contains 5 tables and 13 figures.)