Houston – Two children were found dead under a neighbour's house on Sunday after their mother matter-of-factly told someone helping her move that she had drowned them in a bathtub, authorities said.The 30-year-old mother was in custody and not yet charged but "all indications are she is the one who acted alone" in the deaths of her 7-year-old son and 5-year-old daughter, Houston police spokesperson Kese Smith told The Associated Press.Authorities have not yet confirmed a cause of death but said the woman allegedly told an acquaintance that she had drowned the children.Smith said investigators were still interviewing the woman and had not determined a motive. She was turned in to police by the acquaintance, who came upon her throwing away trash in a field, where she allegedly told him she needed help moving right away.When the man asked about her kids, she calmly said she had killed them, Smith said."She was so matter of fact about it he didn't think she was serious. He thought she was joking," Smith said. "He continued to help her pack."Tried burying the childrenSmith said the man eventually realised something was wrong when he asked again and got the same answer. He then drove the woman toward a nearby police precinct and flagged down an officer, Smith said.The mother apparently tried burying the children at first but put them under a neighbour's house when that proved too difficult, Smith said.Authorities were not immediately aware of the woman having any history of mental health problems, Smith said. He said police had been to the home before but for "nothing major".State child welfare officials have previously visited with the family, said Tejal Patel, a spokesperson for the Texas Department of Family and Protective Services. She said she could not disclose the nature of those visits but said a "top to bottom review" of the family will be done.Neighbours told the Houston Chronicle that the family had moved in just a few months earlier."She would just take her kids to the park; that's all everyone saw of them," neighbour Mike Polk told the newspaper.In 2001, Houston mother Andrea Yates drowned her five children ranging in age from 7 years to 6 months in the bathtub of her family's home. She was eventually found not guilty by reason of insanity in July 2006 and sent to a state mental hospital.