•Cross-linguistic difference in the gender-cue strength impacts predictive processing.•Fine-grained gender distinctions are processed differentially in related languages.•Economy, Transparency and Interdependence can account for differences in processing. We tested predictive gender agreement processing in adjective–noun phrases by 45 4- to 6-year-old Russian- and Bulgarian-speaking children using the visual world eye-tracking paradigm. Russian and Bulgarian are closely related languages that have three genders but differ in the nature and number of gender cues on adjectives. Analysis of the proportion and time course of looks to the target noun showed that only Bulgarian children used gender cues to predict the upcoming noun. We argue that the cross-linguistic difference in the gender cue strength is revealed through the operation of economy, transparency, and interdependence in a gender complexity matrix. The documented advantage for Bulgarian children in gender agreement processing and acquisition underscores the need for a comparative language acquisition approach to typologically close languages.