Lapin 360 (1972)

Delia Peletier has been paid to have a child for a wealthy man who wants an heir. She has the baby and turns it over to her "employer," but subsequently decides she wants the child back. She hires three men to kidnap the child. The quartet hides out in the house of Bernard Lapin, a nuclear scientist they believe to be away on business. Lapin returns, however, and becomes romantically involved with Delia. Meanwhile, her three kidnappers turn on her when they learn she actually wants the child and not the ransom money as she claimed.