Caroline Young

In 1993, Young murdered her 4-year-old granddaughter Dail and 6-year-old grandson Darrin in Hayward, Calif. Young, who was caring for both children while their mother served a sentence for drug dealing, stabbed them to death the day their father was to take custody of them. She then stabbed herself in the stomach, but survived. She had no previous criminal record. Sentenced to death.

http://members.tripod.com/~leelah/index196.html
http://abcnews.go.com/sections/us/deathrow/deathrow_women.html