The minister in charge went on TV to say it would not be enforced, he saw it as some sort of reminder. That's direct from the interview he did for the BBC. That is not atypical of his party who like to "send a message" rather than actually do stuff.
If you believe that car seats save kids lives, then it should be enforced, with proper penalties.
It's pathetically easy to enforce.
You send some traffic wardens and "community" police to stand at traffic lights and near schools.
You give them video cameras on tripods, point them at the traffic and fine everyone who breaks this law. Proper fines. Define proper fines as increasing them until 99.9% of people videoed are belted up. You could do mobile phone using drivers at the same time.
Won't happen of course because it won't make as much money as easily as speed cameras or parking fines.
I've not seen the leaflet, but our kids always travel in car seats. And yes we've had a crash where if he hadn't been strapped in properly DS would have been badly hurt.
I don't worry about persuading my kids. Firstly we have programmed DS1 that it is important, so that the time we forgot to do up the straps he became quite upset and we felt bad.
If they throw a strop, then there is the normal set of sanctions varying from ignoring their protests to loss of privileges.
What we need is strongly branded chairs for boys. Why not ones with labelled "Thunderbird Crash Couch" ? Lots of black and yellow, maybe with pictures of rockets and explosions. Maybe a Disney princess girls seat ? Pink fluffy designer seats ?
Actually you could cross an MP3 player with one of these quite cheaply, and have a seat that played their music and kept them safe. Unless you want to be ripped off by Apple, you can by a decent MP3 player for 15 quid. An obvious variation is to stick on one of those irritating little electronic games which will both keep the child quiet as well as happy and safe.