3 kids here, no safety inserts at all. No bike helmets, very little child safety seat usage, very little seat belt use, and they're all still alive!!!
I feel that nature is the very best teacher ever. My application of this is to let nature take its course, except where death or serious injury is likely.
Here's an example; I've always used wood for heat. When any of the kids would get curious about fire, I'd explain the benefits as well as the hazards. A typical 3 year old doesn't understand logic any too well, so after I told said kid what would happen if he touched the stove while a fire was in it, I built a small fire, then simply walked away. Of course, there was a high-pitched shriek, and a kid running to mommy, clutching his hand.
That only happened once. Two things were accomplished with this, first; don't touch the stove when its hot. Secondly, and even more importantly, if mom and dad say to keep your mitts off of something, and you choose to disobey, bad things will happen.
When I explained what would happen if they stuck something into an outlet, they remembered the stove experience, and took dads warning very seriously.
With all the safety rules and devices there are today, no one ever learns first hand how to listen and understand, (and what happens if you don't), and much worse, no one ever learns how to think. We're not even allowed to teach, (unless we're licensed to do so, of course!). If child protective services would have witnessed the above hot stove example, I'd still be in jail. All that is taught is blind obedience to rules and regulations without question.
And we wonder why we're raising a generation of idiots.