J.B.
A mother's helper is usually an older child/younger teen who is not quite ready to baby-sit 100% on her (or his) own. In my area, a mother's helper would be between 10 and 13 years old and would earn about $5 an hour.
Anyone older than that, who can get paid to baby-sit, is not going to work for "mother's helper" pay. In my area, one would expect to pay a college student at least $10 an hour, and that rate goes up the close you get to the city (I'm in the suburbs).