Children’s English vocabulary acquisition is a process of dynamic and fluid emergence as a result of various stimuli in communicative settings. The paper identifies 5 family variables related to child’s lexical trajectory, namely, the linguistic environment at home, children’s relative exposure to the input, quality of child-directed speech (CDS), frequency of parental input and parent-child interaction. Each family variable contributes uniquely to children’s words learning, among which a highly supportive linguistic learning environment is fundamental for children to accumulate more vocabularies and has a significantly positive impact on children’s vocabulary ability. This paper highlights the importance of targeting children’s learning environment in early years as children’s vocabulary acquisition is a strong predictor of later emergent literacy.