Historically, learning for young students has occurred in formal, in-person classroom environments, but the distance learning context has opened a myriad of learning modalities. To this end, we aim to better understand how deploying learning experience design (LXD) approach supports or hinders children's engagement while participating in an online, video based math course. This study operationalized LXD through the integration of evidence-based pedagogical instructional design and human-centered user experience (UX) design. Findings suggest that students' situational interest and mind-wandering significantly mediate the relationship between user experiences and online engagement. These results provide practical implications for how researchers, designers, and instructors can intentionally iterate the learning experience to reduce mind-wandering and sustain children's online engagement with learning theories as we consider the future of online teaching and learning modalities. [This paper was published in: "ICLS2022 Proceedings," International Society of the Learning Sciences (ICLS), 2022, pp. 472-479.]