During interpersonal conversation, both children and adults adapt the basic acoustic-prosodic features of their speech to converge with those of their conversational partner. In this study, 7-to-10- yearold children interacted with a conversational interface in which animated characters used text-to-speech output (TTS) to answer questions about marine biology. Analysis of children’s speech to different animated characters revealed a 29% average change in energy when they spoke to an extroverted loud software partner (E), compared with an introverted soft-spoken one (I). The majority, or 77% of children, adapted their amplitude toward their partner’s TTS voice. These adaptations were bi-directional, with increases in amplitude observed during I to E condition shifts, and decreases during E to I shifts. Finally, these results generalized across different user groups and TTS voices. Implications are discussed for guiding children’s speech to remain within system processing bounds, and for the future development of robust and adaptive conversational interfaces.