Joash OR Jehoash was the only child of Ahaziah and Zibiah [Family].

1 Chr 3:11 Joram his son, Ahaziah his son, Joash his son,. 1 Chr 3:12 Amaziah his son, Azariah his son, Jotham his son,. 2 Ki 11:1 And when Athaliah the mother of Ahaziah saw that her son was dead, she arose and destroyed all the seed royal. 2 Ki 11:2 But Jehosheba, the daughter of king Joram, sister of Ahaziah, took Joash the son of Ahaziah, and stole him from among the king's sons which were slain; and they hid him, even him and his nurse, in the bedchamber from Athaliah, so that he was not slain. 2 Ki 11:21 Seven years old was Jehoash when he began to reign.

One son listed.

Amaziah¹.