Children can learn words incidentally from stories. This kind of learning is enhanced when stories are presented both aurally and in written format, compared to just a written presentation. However, we do not know why this bimodal presentation is beneficial. This study explores two possible explanations: whether the bimodal advantage manifests online during story exposure, or later, at word retrieval. We collected eye-movement data from 34 8-to 9-year-old children exposed to two stories, one presented in written format (reading condition), and the second presented aurally and written at the same time (bimodal condition). Each story included six unfamiliar words (non-words) that were repeated three times, as well as definitions and clues to their meaning. Following exposure, the learning of the new words' meanings was assessed. Results showed that, during story presentation, children spent less time fixating the new words in the bimodal condition, compared to the reading condition, indicating that the bimodal advantage occurs online. Learning was greater in the bimodal condition than the reading condition, which may reflect either an online bimodal advantage during story presentation or an advantage at retrieval. The results also suggest that the bimodal condition was more conducive to learning than the reading condition when children looked at the new words for a shorter amount of time. This is in line with an online advantage of the bimodal condition, as it suggests that less effort is required to learn words in this condition. These results support educational strategies that routinely present new vocabulary in two modalities simultaneously.