My brother drives for Yellow Cab in SF and he tells me the company policy is to require parents to provide a safety seat or to refuse the child passenger. I believe in California the law allows for the DRIVER of a vehicle carrying an unrestrained child to be cited. Mind you, he also says for a big enough tip, you can probably find a driver willing to bend the rules. He won't - he used to work in a hospital emergency room and is a big fan of child safety seats.