My Daughter's Keeper (1991)

She makes the breakfast. She makes the beds. She makes love to the husband... She's much more than just a nanny.

An American writer in England takes his children and a newly hired nanny on a trip to South Africa while his wife, a reporter, is on assignment. He has an affair with the nanny, but when he refuses to leave his wife for her, the nanny gets her revenge by kidnapping his children.