We assess the effects of the Crianza Positiva text and audio e-messaging program on caregiver-child language interaction patterns. The program is a six-month-long intervention for families with children aged 0-2 aimed at strengthening parental competences. Its design exploits behavioral tools such as reminders, suggestions of action, and messages of encouragement to reinforce and sustain positive parenting practices. Families in 24 early childhood centers in Uruguay that completed an 8-weeks workshop were randomized into receiving or not receiving mobile messages. After the program, we videotaped 10-minutes-sessions of free play between the caregiver and the child, and decoded language patterns using automated techniques. The intervention was successful at improving the quality of parental vocalizations, as measured by the parent's pitch range. We also found suggestive evidence of increases in the duration of adult vocalizations. Results are consistent with more frequent parental selfreported involvement in reading, telling stories and describing things to the child. Regarding the child, we find a non-robust decrease in the duration of vocalizations, which we attribute to a crowding-out effect by the caregiver in the context of a fixed 10-minute suggested activity and a more proactive parental role.