I have a CERN car to drive to a workshop on the Prévessin site. During the lunch break, I need to drive to Ferney-Voltaire to collect one of my kids from school. Is it okay for me to use the CERN car for that short distance?

No. CERN vehicles are provided to members of the personnel within the framework of their work for CERN and solely for official use.  Use of such vehicles for personal reasons is strictly forbidden (see Operational Circular No. 4). Moreover, CERN car insurance will cover only professional use.