Children with Down syndrome (DS) are at higher risk for both delayed expressive language and poor speech intelligibility. The current study utilized the quantitative automated language environment analysis (LENA) to depict mother and child vocalizations and conversational patterns in the home of 43 children with DS, chronologically aged 24-64 months. Children with DS displayed fewer utterances than typically developing children; however, there was wide variability. Furthermore, children with DS did not show increased vocalization counts across their chronological ages. In contrast to previous findings, this study found that the mothers of children with DS had a reduced number of vocalizations. However, the vocalizations increased with age in comparison to mothers of typically developing children. Implications for targeted interventions that facilitate learning opportunities in bidirectional contexts for children with DS and their parents are discussed, with particular attention to quantify behavioral phenotypes utilizing a novel expressive language assessment tool.