The ability for a child to explain what he or she is thinking is crucial for their language development. This study focused on children in pre-kindergarten and kindergarten at a university-affiliated elementary school in Southern California and the relationship between their explanatory discourse abilities and their scores on topic vocabulary and picture identification tasks. This study also explored how home discourse practices influence children’s explanatory discourse abilities. The aims of this study were to evaluate the relationship between vocabulary knowledge and their performance on one oral explanation task around the topic of teeth cleaning. The quality of a child’s oral explanation skills is scored on three features: the sophistication of their topic vocabulary, the sophistication of their sentence structure, and the coherence and cohesion of their discourse. Findings suggest that uncommon words knowledge and general vocabulary knowledge positively influence children’s sentence structure skills. We also find that the more frequently parents talk with their children about things they have done together positively influences children’s vocabulary and cohesion/coherence skills. This study adds to previous literature on oral language development by examining a unique genre of oral language, explanatory discourse.