Guess for kids, you'll have to start real young...my friend's boy started the car seat since 1 month+ old (even when I go and pick her to go out, she'll bring along the car seat)... since then, not trouble as the kids thinks it's part an parcel of travelling in car (he's 2yrs + now)
the other friend start late and initially her kid makes noise and cry. So what she do is to cancel the outing an go home. After a few times, the child know that it's either be good and take the car seat or no outing.
Jackpot! - safety first in the minds of the parents, start young with their minds as awareness!