Emotion regulation (ER) is key for children's development and it has recently been considered in many serious games and e-learning technologies. However, these tools have focused on children's efforts to change their own emotions (intrapersonal ER), overlooking how children may engage in modifying the emotions of others (interpersonal ER). To address this gap, we have developed a multiplatform online serious game, Emodiscovery, which evaluates whether children (8-11 year-olds) tend to use different adaptive and maladaptive regulation strategies to change others' negative emotions with the use of 3D animated characters. The game is organized into levels, each representing a different scenario, where the child is asked to interact with the character three times choosing an appropriate regulation strategy to cheer him or her up from four possible options, being two adaptive and two maladaptive strategies. To test the effectiveness of the game, a sample of English children played three scenarios depicting a character feeling sadness, anger, and fear, respectively. Results showed that most children chose adaptive strategies to improve the character's emotion across the different emotion scenarios. Furthermore, emotion recognition was not positively related to children's choices of regulation strategies. The implications and applications of the games are discussed.