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.
You’ll notice that none of that liability coverage pays for your car or injuries, nor for any injuries your passengers sustain if you cause a wreck. This is why many people — particularly those whose car isn’t yet paid off — want “full coverage” car insurance. This isn’t actually a type of coverage, but instead typically refers to policies that include liability coverage, plus comprehensive and collision coverages.
To reduce the insurance premium, the insured party may offer to pay a higher excess (deductible) than the compulsory excess demanded by the insurance company. The voluntary excess is the extra amount, over and above the compulsory excess, that is agreed to be paid in the event of a claim on the policy. As a bigger excess reduces the financial risk carried by the insurer, the insurer is able to offer a significantly lower premium.
A compulsory car insurance scheme was first introduced in the United Kingdom with the Road Traffic Act 1930. This ensured that all vehicle owners and drivers had to be insured for their liability for injury or death to third parties whilst their vehicle was being used on a public road. Germany enacted similar legislation in 1939 called the "Act on the Implementation of Compulsory Insurance for Motor Vehicle Owners."