If you fear losing your children, why would you murder them?

That really depends. Some people have the notion of, "if I can't have it, nobody will" and fail to see the difference between a chair and a child. Some do so because they are certain the child will live a miserable life - Goebbels and his wife killed their eight (?) children in Hitler's bunker because they knew that the children would be d, tortured, and sent to Siberia by the Soviets because of who their parents were and they felt that was a fate worse then death. Some people are just plain sick.