Albert Barnes Commentary 2 Kings 14:6

"but the children of the murderers he put not to death; according to that which is written in the book of the law of Moses, as Jehovah commanded, saying, The fathers shall not be put to death for the children, nor the children be put to death for the fathers; but every man shall die for his own sin." — 2 Kings 14:6 (ASV)

The children of the murderers he did not kill - This seems to be noted as a rare instance of clemency (compare the note on 2 Kings 9:26). It is strange at first sight that, when the Law contained so very plain a prohibition (see marginal references), the contrary practice should have become established. But we must remember, first, that this was the general custom in the East ; and secondly, that it had the sanction of one who might be thought to have thoroughly known the mind of the legislator, namely, Joshua .