Preschool-aged children develop awareness of the words theydo and do not know. Awareness of one’s lexicon mayencourage word learning if children pay more attention to thedefinition of unknown words. Here, we tested 3-4-year-oldchildren (N = 91) on a word learning task embedded in an e-book. When a novel word was read, children were eitherasked if they knew the word, asked a question about thestoryline, or asked no question. Then they were given adescription without visual input and asked to identify thereferent’s picture from three choices. Participants who wereasked if they knew a word before being provided with thedefinition identified more referents than children in the otherconditions. Children’s word learning was predicted by short-term memory.