This paper presents a simple and efficient capacitive sensing system suitable for detecting presence of a child in an infant car seat. It also details a warning system that alarms the parents once a child is found to be left alone in a car. Infant seat with child is, usually, kept (safely) in the rear seat. Driver and passengers, in some situations, may leave the car without taking (forgetting) the child. When a car is turned-off (windows closed) temperature inside it will increase rapidly and can be life threatening as the thermoregulatory system of child is weak. Such incidents have been reported worldwide. The proposed capacitive sensor system detects child occupancy. The system also has a warning unit. Once the car is turned-off and a child is found to be left alone in the car (in an infant seat) the unit first generates an audio alarm. After a preset time, if no one takes the child, it will automatically dial (using a GSM module) to parents or driver to help the child. A prototype of the proposed capacitive sensor and warning system have been built and tested. The developed sensor accurately detected presence of a child (in various postures) in an infant seat. It also distinguished a child from other objects such as milk/water bottles, toys, bags, etc. Results showed that the developed system is very efficient and reliable.