Zakieya L. Avery, 28, was charged Saturday with two counts of first-degree murder and two counts of attempted first-degree murder, Montgomery County Police said in a statement.
A second woman, who was briefly hospitalized after the incident, was also charged in the two deaths. Police believe she is not related to the family, but lived at the same residence in Germantown.
Norell Harris, 1, and his sister, Zyana Harris, 2, suffered fatal stab wounds while their siblings, ages 5 and 8, were hospitalized with injuries, authorities said.
"Cases like this are heartbreaking," county Police Chief Tom Manger said. "Our thoughts are with the family and friends of the victims."
Police said they found the four children Friday morning after a neighbor called 911 to report suspicious activity at the home. The neighbor reported seeing a car with a door open and a knife next to it.
Exorcism is a ritual aimed at defeating purported evil spirits or demons. Authorities did not provide additional details on why they suspected exorcism.