God does not think that killing children is okay, even when it is in sacrifice for his worship.
‘Hear the word of the Lord , you kings of Judah and people of Jerusalem. This is what the Lord Almighty, the God of Israel, says: Listen! I am going to bring a disaster on this place that will make the ears of everyone who hears of it tingle. 4 For they have forsaken me and made this a place of foreign gods; they have burned incense in it to gods that neither they nor their ancestors nor the kings of Judah ever knew, and they have filled this place with the blood of the innocent. 5 They have built the high places of Baal to burn their children in the fire as offerings to Baal—something I did not command or mention, nor did it enter my mind. ~ Jeremiah 19:3-5, NIV
They have built the high places of Topheth in the Valley of Ben Hinnom to burn their sons and daughters in the fire--something I did not command, nor did it enter my mind. ~ Jeremiah 7:31
They sacrificed their sons and daughters in the fire. They practiced divination and sought omens and sold themselves to do evil in the eyes of the LORD, arousing his anger. ~ 2 Kings 17:17
They built high places for Baal in the Valley of Ben Hinnom to sacrifice their sons and daughters to Molek, though I never commanded--nor did it enter my mind--that they should do such a detestable thing and so make Judah sin. ~ Jeremiah 32:35
According to the Bible, the concept of killing children as sacrificial offerings was a "detestable thing" - it didn't even come up in his heart - and made those who practice it worthy of destruction at God's hands. Would it be any less detestable in God's eyes for JWs to sacrifice their children on the altar of the blood transfusion doctrine?
Now, I know you're discussing "god" killing children, at Armageddon™ or for such heinous crimes as teasing a bald-headed prophet. But those passages show that "god" disapproves of killing innocent children. However, those passages should give any JW with an active brain stem a jolt, one that might make them have second thoughts about signing their blood cards or the blood cards that their children carry. Those passages can plant a seed, even though you're on a completely different topic at the time.