Albert Barnes Commentary 2 Chronicles 24:1

"Joash was seven years old when he began to reign; and he reigned forty years in Jerusalem: and his mother`s name was Zibiah, of Beer-sheba." — 2 Chronicles 24:1 (ASV)

This chapter is parallel with 2 Kings 12, but it treats the matters common to both narratives in a different and, apparently, supplemental way.