A 30-year-old Texas woman was in custody Sunday, accused of having killed her two children and placed their bodies beneath a neighbor's home, authorities said.

The woman, who was not identified, had not yet been charged, but she told homicide investigators that she killed her 7-year-old daughter and 5-year-old son, Houston police spokesman Kese Smith told NBC News.

Smith said it appeared that the woman drowned the children in a bathtub Friday. After trying to bury them, she "hid them under the neighbor's house," Smith said. "The neighbors were unaware."

The woman apparently confessed to authorities after telling an acquaintance Sunday morning that she needed to immediately move from her home, a few miles south of downtown Houston, Smith said.

As they were placing things in the back of her truck, Smith said, the acquaintance — an unidentified man —asked about her kids.

"That's when she was very matter of fact," Smith said. "She stated: I killed them. She was so matter of fact, he didn't think she was serious."

As they were leaving, Smith said, the man asked about her children again, and she said she already told him that she had killed them.

"He then drove her to nearby patrol station," Smith said.

The woman has a 12-year-old boy who is unharmed, Smith said, adding that a motive remains unclear and that the woman has no apparent history of mental illness.