Why does the Psalmist speak about killing children?
"How blessed will be the one who seizes and dashes your little ones against the rock," (Psalm 137:9).
Critics often bring up this verse as an attack on the validity of the Bible. Usually, it is out of context. Still, does the Bible teach that it is okay to kill children? The answer, of course, is no it doesn't. But we must ask what the Psalmist was saying and what he was saying it.
The context of Psalm 137 is the Babylonian captivity. The Psalmist speaks of the captors tormenting the people of God (vv. 1-3), a promise to remember Jerusalem (vv. 5-6), and a curse against the captors (vv. 7-9).
The Psalmist is in exile and had probably witnessed the atrocities committed against his people, babies included. In the revenge-style that was so common at the time, he wishes the same upon his enemy as a description of their utter destruction. Is God approving of this retribution? There is nothing in the text to suggest he did.
It is worth noting that the Old Testament records many atrocities. The fact is that God allowed people their sinful desires and he worked within their culture, even as he does now, as he permits all kinds of bad things to happen. Nevertheless, God introduced what is called the Apoditic Law (Exodus 21:24): an eye for an eye and a tooth for a tooth. The Apoditic Law was instituted to prevent the increase of blood revenge, a practice where revenge would escalate out of control between two parties. Since the hearts of the fallen are so wicked and the harsh environment and culture produced difficulties for survival, God has a few options to counter their proclivity towards evil. He can run roughshod over their free will and force everyone to obey him, or he could wipe them all out (he had already done this with Noah's flood), or he could work within the situation at hand. In the case of this psalm, and it's Babylonian captivity context, God chose to work with people and through them instead of violating the freedom he had given them and forcing them to act in a manner that he instructs. Therefore, the Psalmist is expressing his curse against Babylon, a natural response to what his people have already suffered.