Early vocabulary development benefits from diverse lexical exposures within children's language environment. However, the influence of lexical diversity on children as they enter middle childhood and are exposed to multimodal language inputs remains unclear. This study evaluates global and local aspects of lexical diversity in three 1.6-million-word child-directed corpora, representing average Chinese children's speech, print, and media language environments. Additionally, pseudo-multimodal samples were compiled from the three corpora to compare with the unimodal environments on lexical diversity. We then investigated the associations between lexical diversity and the acquisition of 361 words spanning early-to-middle childhood. The findings show that print and pseudo-multimodal language provided the most diverse lexical environments, whereas speech exhibited the least diversity. However, speech diversity most strongly predicted lexical development, particularly before the onset of middle childhood. Exploratory analysis revealed that lexical diversity of other modalities emerged as stronger predictors thereafter. Early lexical development was best predicted by words' variations in connectivity with other words within an immediate context, whereas in middle childhood, variations in words' occurrences in larger context windows became the primary predictor, implicating children's growing ability to attend to linguistic contexts of increasing sizes. Importantly, higher diversity was consistently associated with earlier word acquisition across measures and developmental phases. These findings underscore the critical role of varied lexical experiences in children's language development.