A series of experiments conducted in Central Europe (Hungary, Austria) and East Asia (Japan) probed whether 5- to 10-year-old children (n = 436, 213 female) and adults (n = 71, 43 female; all data collected between July 2020 and May 2023) would infer traits and choose partners accordingly, in a novel touchscreen game. The participants observed third-party actions and interactions of animated agents whose behavior varied in prosociality and skill, and subsequently selected whom to play with in potentially cooperative endeavors. Overall, the results indicate (1) that trait inference may not naturally follow from action understanding but relies on learning and experimental task framing, and (2) that by 7 years of age, children begin to capitalize on such inferences in partner choice.