Marian Robinson, 70, says she cares for the Obamas' two daughters, Malia, 9, and Sasha, 6, while her son-in-law seeks the Democratic presidential nomination, The Boston Globe reported Sunday.
She told the newspaper she remembers telling her children, "Look, you see, I am raising my kids, so don't you all have any kids that you expect me to help you raise."
Now though, she said she cannot imagine somebody else caring for her grandchildren while their father runs for president.
"If somebody's going to be with these kids other than their parents," she said, "it better be me."
Her daughter, Michelle Obama, 44, said at a campaign stop last month that it is a relief to her to know that her mother is caring for her children while she and her candidate husband are on the road, the newspaper reported.
"I am standing here breathing in and out with any level of calm because my 70-year-old (mother) is home with my girls," she told voters in Chillicothe, Ohio. "There's nothing like grandma."