It's not stated in those particular passages, no. However, taking in the context of the books of Samuel, Kings, and Chronicles, the pattern of co-regency in Judah is easily established as is the chaotic power transitions of Israel. The precedent was established in David's line for the southern kingdom of Judah when he placed Solomon in power a substantial amount of time before his death (1 Kings 1-2). See also 2 Kings 8:16 where Jehoshaphat and his son Jehoram reigned together as well as 2 Kings