No. 6 is staggeringly evil. Wait until the child who lived is old enough to understand. He (or she) will certainly feel guilt that his two siblings were killed and he lived. What will he think about mommy? This is one of the single most evil acts ever.
No. 6 was terribly evil.
It amazes me that anyone could be that callous.
I envision a child who lives in daily fear of being a "burden" to mommy, leaving home as soon as possible to escape the fear.