The two girls, ages 8 and 10, were left behind to take care of themselves and get back and forth from school, the Austin (Texas) American-Statesman reported Monday.
The mother, Kristine Noffsinger, 29, was charged with two counts of abandoning a child and was held on $40,000 bond, police said.
The children told investigators their mother had left for St. Louis April 17, an arrest warrant said. A child protective services investigator said the children were found alone in their apartment in Round Rock on April 18.
An investigator tried to call Noffsinger on April 18, but she didn't answer or call back until the next day.
The children said their mother had put the family pet into an animal care facility while she was gone.
The girls said they had recently moved to Texas from Illinois and didn't have family in the state.
The child protection agency has taken custody of the children.