A seat occupant sensing apparatus includes a notched foam bottom seat cushion and a pressure-responsive sensor disposed between the bottom cushion and a frame of the seat. The notch is a narrow channel on the underside of the foam cushion that extends upward into the foam to limit and direct dispersion of occupant loading through the cushion. A rectangular notch smaller in dimension than a child seat frame is formed in a central region of the foam cushion, and a fluid-filled bladder or other force-responsive sensor mat is disposed substantially within the perimeter of the notch. The sensor will detect a normally seated occupant due to the relatively uniform seat load, but will not detect a cinched-down child seat because the notch limits dispersion of child seat loading in the direction of the sensor.