'Pledges' in the Bible

and hath taken all the gold and the silver, and all the vessels that are found in the house of Jehovah, and in the treasures of the house of the king, and the sons of the pledges, and turneth back to Samaria.

Now therefore, I pray thee, give pledges to my lord the king of Assyria, and I will deliver thee two thousand horses, if thou be able on thy part to set riders upon them.