  Mathematical language is a cornerstone of a child's mathematical development,
and children can effectively acquire this language through storytelling with a
knowledgeable and engaging partner. In this study, we leverage the recent
advances in large language models to conduct free-form, creative conversations
with children. Consequently, we developed Mathemyths, a joint storytelling
agent that takes turns co-creating stories with children while integrating
mathematical terms into the evolving narrative. This paper details our
development process, illustrating how prompt-engineering can optimize LLMs for
educational contexts. Through a user study involving 35 children aged 4-8
years, our results suggest that when children interacted with Mathemyths, their
learning of mathematical language was comparable to those who co-created
stories with a human partner. However, we observed differences in how children
engaged with co-creation partners of different natures. Overall, we believe
that LLM applications, like Mathemyths, offer children a unique conversational
experience pertaining to focused learning objectives.
