In recent years, there has been a growing emphasis on using computational thinking (CT) to teach mathematical concepts. The integration of math+CT enables students to gain a deeper understanding of both mathematical and computer science (CS) concepts. Although numerous professional development programs provide teachers with a solid understanding of CT and methods for integrating it into the curriculum, there has been little research on how teachers apply this knowledge to the design and development of math+CT activities. Moreover, the majority of integrated activities are concentrated in the upper elementary grades, while the early grades (i.e., K-2) remain underexplored. The purpose of this study is to describe how teachers translate their CT knowledge in the collaborative design of an integrated math+CT activity focused on number sense and mathematical operations for grades K-2. Research faculty from the CS and Teacher Education departments designed block-based programming activities for K-2 students to explore and make sense of place value representations of the numbers 1 - 1000. In-service elementary teachers in an online graduate STEM CT course (N = 13) experienced these activities as learners and provided feedback for redesign from their perspectives as classroom teachers. Qualitative analysis of collaborative problem-solving slides and individual reflections revealed how teachers connected their mathematical knowledge for teaching place value to their emergent understanding of CT concepts of abstraction, decomposition, and debugging. This research bridges the gap between enthusiasm for math+CT integration and teacher capacity to use CT to promote creative mathematical thinking and problem-solving in K-2 classrooms.