If your son, daughter, wife, husband or any other policyholder on your cover makes a claim, or a claim is made against them, while they're driving their own car it won't affect any of the other policyholders' No Claims Bonus. However, if they have an accident in your car (which you are policyholder for) then your No Claims Bonus will be affected, but not for the other cars.
Vehicle insurance (also known as car insurance, motor insurance, or auto insurance) is insurance for cars, trucks, motorcycles, and other road vehicles. Its primary use is to provide financial protection against physical damage or bodily injury resulting from traffic collisions and against liability that could also arise from incidents in a vehicle. Vehicle insurance may additionally offer financial protection against theft of the vehicle, and against damage to the vehicle sustained from events other than traffic collisions, such as keying, weather or natural disasters, and damage sustained by colliding with stationary objects. The specific terms of vehicle insurance vary with legal regulations in each region.