My dcs have always been really good near the roads, always stop when asked and never run accross, we live in a busy city. Only a couple of time lately ds aged 6 has been a bit silly, letting go of dh's hand and running accross (which I let him do when I say, but this was without permission). We were out for the day and to be 'funny' my ds ran across a small road without looking, near a corner, and seconds later a car came speeding around. Any sooner and it would have got ds who was oblivious as was busy with na na na na ner behaviour.
When we got home I showed him a car accident on Liveleak where someone got run over, not too graphic and only enough to get the gist.
Is that a bit much for a six year old? Only he's my oldest of three with another on the way and they can't all hold the pushchair!