California recently passed a new law requiring Rear Facing seats until 2 years of age. Personally, I find that to be insane. Both of our children were itching to be tuned around and become part of the social circle in the car far before they even turned 1. In addition, my 2 year old has her feet against the back of the passenger seat already. She would be far too tall for rear facing up to 4. I can't imagine that a rear facing seat would fit in most cars for children up to 4. They would have to be folded up like Swiss army knives. I'm all about protecting children, but part of that has to come down to parent and driver responsibility. There needs to be some reasonability built in to these considerations.
As it is, a high percentage of drivers in and around central Cali don't even use carseats or seatbelts at all!
And, as a curiousity, because I've never had to do it, what to people do to restrain children on public transport, trains, etc... I'm guessing nothing.
All opinions, including this one, are inherently biased. Seek information broadly and think for yourself!