Living in San Francisco I've not seen the taxi exemption for California anywhere. New York City taxis are exempt like most of Europe.

My kid is too young for a booster city. It's pretty impractical to take a child seat or booster with you unless you plan to hire a car the other end. When I travel back to see my family in Europe I take the train from the airport. So we bus and Bart to the airport even though it would be much easier with luggage to take a taxi.