A parent is “liable for an injury caused by the child where the parent’s negligence made it possible for the child to cause the injury complained of, and probably that it would do so.” http://law.justia.com/cases/california/court-of-appeal/2d/116/310.html. Thus, if a parent is aware that a child has bad brakes on his bike, or is aware that he drinks under age, can be liable if injury results to a third party.  This theory of liability is called “Negligent Supervision.”  https://www.justia.com/trials-litigation/docs/caci/400/