Police in Elko, Nev., had reported Lillyanna Ramirez, 9, and Martin Angel Rosales II, 3, missing and the California Highway Patrol issued an Amber Alert for them, The Sacramento Bee reported.
Authorities had believed the children were with their mother, Amber Schenck, 29, and Martin Cisneras Rosales, 33, the father of the boy, but only Schenck turned herself in, the newspaper said. Rosales' whereabouts was unknown, the newspaper said.
The children had been in the care of Child and Family Services in Elko when Schenck and Rosales allegedly took them, the newspaper said.
"We are going to pursue criminal charges against the suspects, but currently we have no warrants" for their arrests so neither was in custody, Elko police Capt. Will Lehmann said. "They have a history of domestic violence and substance abuse."