Jehoiada organizes the coup and crowns Joash

In the seventh year the priest arms a coalition around a child

Jehoiada strengthens himself and takes captains of hundreds into covenant: Azariah son of Jeroham, Ishmael son of Jehohanan, Azariah son of Obed, Maaseiah son of Adaiah, and Elishaphat son of Zichri. They gather Levites from the cities of Judah and the chief of the fathers of Israel to Jerusalem. All the congregation make a covenant with the king in the house of God: the king's son shall reign, as the LORD hath said of the sons of David.

The hidden child is now the center of a planned transfer of power. Chronicles expands the Levite role beyond Kings. Sacred personnel and Davidic promise are the coalition's language. That does not make the boy a mascot to be paraded. He is still the child who has been in hiding since the massacre.

Sabbath courses, David's weapons, and a death order fill the courts

A third part of the entering sabbath priests and Levites are to be porters of the doors, a third at the king's house, a third at the gate of the foundation; all the people in the courts. None is to come into the house of the LORD save priests and ministering Levites. The Levites are to compass the king, every man with his weapon; whosoever else comes into the house shall be put to death. Jehoiada does not dismiss the outgoing courses. He delivers spears, bucklers, and shields that had been king's David's, kept in the house of God. Armed people stand from the right side of the temple to the left, by the altar, round the king.

Then they bring out the king's son, put the crown on him, give him the testimony, and make him king. Jehoiada and his sons anoint him and say, God save the king. The testimony given with the crown is some covenant or royal document; its exact form is not described. A child under armed guard in a death-marked court is not a children's-story coronation, and a successful temple coup is not a standing warrant for clergy to seize a government or to place a child in the path of swords.