Children with developmental disabilities benefit from their language environment as much as, or even more than, typically developing (TD) children, but maternal language directed to developmentally delayed children is an underinvestigated topic. The purposes of the present study were to compare maternal functional language directed to children with two developmental disabilities – autism spectrum disorder (ASD) and Down syndrome (DS) – with TD children and to investigate relations of maternal functional language with child language skills. Participants were 60 mothers and their children with TD (n = 20), DS (n = 20), or ASD (n = 20). Children's mean developmental age was 24.77 months (SD = 8.47) and did not differ across the groups. Mother and child speech were studied during naturalistic play. We found (a) similarities in maternal functional language directed to the two groups of children with developmental disabilities compared to that directed to TD children and (b) a positive association between subcategories of information-salient speech and child mean length of utterance in TD dyads only. The clinical and developmental implications of these findings are discussed.