Debugging is an over-looked component in K-12 computational thinking education. Few K-12 programming environments are designed to teach debugging, and most debugging research were conducted on college-aged students. In this paper, we presented debugging exercises to 6th-8th grade students and analyzed their problem solving behaviors in a programming game--BOTS. Apart from the perspective of prior literature, we identified student behaviors in relation to problem solving stages, and correlated these behaviors with student prior programming experience and performance. We found that in our programming game, debugging required deeper understanding than writing new codes. We also found that problem solving behaviors were significantly correlated with students' self-explanation quality, number of code edits, and prior programming experience. This study increased our understanding of younger students' problem solving behavior, and provided actionable suggestions to the future design of debugging exercises in BOTS and similar environments.