Learning about emotions is an important part of children's social and communicative development. How does children's emotion-related vocabulary emerge over development? How may emotion-related information in caregiver input support learning of emotion labels and other emotion-related words? This investigation examined language production and input among English-speaking toddlers (16-30 months) using two datasets: Wordbank (N = 5520; 36% female, 38% male, and 26% unknown gender; 1% Asian, 4% Black, 2% Hispanic, 40% White, 2% others, and 50% unknown ethnicity; collected in North America; dates of data collection unknown) and Child Language Data Exchange System (N = 587; 46% female, 44% male, 9% unknown gender, all unknown ethnicity; collected in North America and the UK; data collection dates, were available between 1962 and 2009). First, we show that toddlers develop the vocabulary to express increasingly wide ranges of emotional information during the first 2 years of life. Computational measures of word valence showed that emotion labels are embedded in a rich network of words with related valence. Second, we show that caregivers leverage these semantic connections in ways that may scaffold children's learning of emotion and mental state labels. This research suggests that young children use the dynamics of language input to construct emotion word meanings, and provides new techniques for defining the quality of infant-directed speech.