Here are examples of various states law:
New York City
In the New York City Taxi and Limousine Commission , it states
Drivers of yellow medallion taxicabs and for-hire vehicles and their passengers, are exempt from laws regarding car seats and seatbelts. Keep in mind, the TLC encourages everyone in the vehicle to buckle their seatbelts while riding in a cab. There are no Taxi and Limousine Commission rules regarding this, as it is a State exemption. Passengers with children are encouraged to bring their own car seats, which the drivers must allow passengers to install.
*NOTE - Children under the age of seven are permitted to sit on an adult’s lap.
http://www.nyc.gov/html/tlc/html/passenger/faq_pass.shtml
Washington State
Far West Cab (206) 622-1717 *
Orange Cab (206) 522-8800 *
These are cab companies that seem to be able to provide car seat if required. But beware of expired car seat.
Hard to find out if it is legal or illegal from the government websites.
State of Nevada
The Nevada child car seat law NRS 484.474 Effective on June 1, 2004. Has the following summarized provisions: (Read about the complete law here.)
NRS 484.474
Child less than 6 years of age and weighing 60 pounds or less to be secured in child restraint system while being transported in motor vehicle; requirements for system; penalties; exceptions. [Effective June 1, 2004.]
1. Except as otherwise provided in subsection 5, any person who is transporting a child who is less than 6 years of age and who weighs 60 pounds or less in a motor vehicle operated in this state which is equipped to carry passengers shall secure the child in a child restraint system which:
(a) Has been approved by the United States Department of Transportation in accordance with the Federal Motor Vehicle Safety Standards set forth in 49 C.F.R. Part 571;
(b) Is appropriate for the size and weight of the child; and
(c) Is installed within and attached safely and securely to the motor vehicle:
The provisions of subsections above do not apply:
(a) To a driver or passenger who possesses a written statement by a physician certifying that he is unable to wear a safety belt for medical or physical reasons;
(b) If the vehicle is not required by federal law to be equipped with safety belts;
(c) To an employee of the United States Postal Service while delivering mail in the rural areas of this state;
(d) If the vehicle is stopping frequently, the speed of that vehicle does not exceed 15 miles per hour between stops and the driver or passenger is frequently leaving the vehicle or delivering property from the vehicle; or
(e) To a passenger riding in a means of public transportation, including a taxi, school bus or emergency vehicle.
Travel Vest for kids
If you a have a kid that is above 3 years old, you can use Travel Vest for kids. It is an alternative to booster seats, the RideSafer Travel Vest substantially increases the level of safety with exceptional crash test results. It also provides ease of use and flexibility for parents while providing more comfort for children. Research respondents overwhelmingly approved the Travel Vest and indicated that it provide excellent and superior solutions to many problems associated with currently available booster seats. The RideSafer can be used in the left, right, or center rear seats, moves easily from vehicle to vehicle on your children, and best of all, it meets or exceeds all standards of the FMVSS 213 (Federal Motor Vehicle Safety Standard).