Over the last decade or two there have been places where children have been killed in civil wars. They have been shot, chopped up, burned, starved, you name it and the methods all had the same result--dead children.
So there are many of us who wonder why it took chemical weapons to get people to take notice.
Was the kid killed by gun shot in Syria somehow not as dead as the kid who was killed with gas?
We can take a "moral" high ground and say that a message needs to be sent. But it appears the message might be that it is okay to kill a lot of kids as long as you don't use gas, or you can excuse it because their deaths were simply collateral damage.
A dead child is a dead child.