This article describes the theory-informed design of the "ELENA goes shopping" mobile game and reports on the evaluation of its effectiveness through a design research approach. The game aimed to foster young children's (aged 4-8) interest in a neighboring (geographically proximate) language and to familiarize them with its sounds, pronunciation and vocabulary. Additionally, it strived to involve adults in young children's language learning activities. To achieve these objectives, the game connects playful learning activities to an accessible, familiar real-world setting (supermarket). The game was developed and evaluated through three iterative design research cycles. First, interdisciplinary experts (n = 8) evaluated the game by means of a questionnaire and focus group discussion. In the second and third cycles, the game's feasibility and usability was evaluated via questionnaires, semi-structured interviews and a language learning outcome test. Results revealed that children (34) and adults (14) alike found the game useful for familiarization with and motivation to learn another language, and feasible to involve adults. Nevertheless, children could play the game autonomously with minimum adult assistance. A dependent t-test on a repeated vocabulary test revealed adults' and children's perception that the game helped them familiarize with another language to be consistent with test results. A limitation to this study is that the test was administered immediately after game playing. Future studies could explore effects of "real-world" contextualization on early second language learning and vocabulary recall by measuring after longer time spans and compare results versus a non-contextualized game.