The woman's husband came home and found the children's bodies and his wife with slashed wrists, the Philadelphia Daily News reported. Sources told the newspaper the woman had written notes to her husband saying she believed he was having an affair.
Police did not release the name of the woman, who was taken into custody, but neighbors identified her as Stacey Newkirk, 41. They said the 18-month-old twins were named Adam and Eve.
Their 4-year-old sister was reported in stable but guarded condition at St. Christopher's Hospital for Children.