Before you can use commonsense, you need information, if you don't know smoking or drinking is harmful to the unborn baby, you don't know it's commonsense not to do it.

Leaded paints were not the problem, you have to ingest an awful lot of lead, over  a very long period, to become ill,

But not much has to be ingested to cause mild or medium mental retardation

As for childproof lids, well they had something better in those days, it was called common sense. Medicine and harmful substances were kept out of reach, and the problem was solved.

So it was just too bad for those children who were made ill or died because of a lack of commonsense by an adult or sometimes a small lapse of concentration, mustn't introduce a simple way of avoiding that as it would just be mollycoddling.

How on earth can you say that relying on commonsense was better than a simple method of avoidance?

If you were having an operation in hospital, would you be happy to know that you were relying solely on commonsense to still be alive afterwards or would you prefer that safety procedures were in place?

seatbelts became a necessity because of the increased speed performance of cars, and the increase of the number of cars on our roads.

Nonsense, seatbelts were introduced after research showed their effectiveness at reducing death and injury at all speeds, 10 - 20mph was enough to put a driver's face through a windscreen.

http://www.roadsafetyobservatory.com/HowEffective/vehicles/seat-belts

There was absolute shame, and the Parents of these  juveniles had to live with it.

I can assure you that not everybody felt shame, not all parents were fine upstanding citizens

I'd say it depends on a lot more then social class. Accidental deaths may have halved, (you say that, and I haven't managed to get any data to support or deny it)

http://www.poverty.org.uk/23/index.shtml

It would seem that the golden haze of nostalgia is rather apt to cloud minds.