Most common words in English have multiple different meanings, but relatively little is known about why children grasp some meanings better than others. This study aimed to examine how variables at the child-level, wordform-level, and meaning-level impact knowledge of words with multiple meanings. In this study, 174 children aged 5- to 9-years-old completed a test of homonym knowledge, and measures of non-verbal intelligence and language background were collected. Psycholinguistic features of the wordforms tested were assessed through collecting adult ratings, corpus coding, and using existing databases. Logistic mixed effects models revealed that whilst the frequency of wordforms contributed to children's knowledge, so also did dominance and imageability of the separate meanings of the word. Predictors were similar for children with English as an Additional Language and English as a first language. This greater understanding of why some word meanings are known better than others has significant implications for vocabulary learning.