I'm talking about unsupervised up and down the pavement play. We live on the sort of road you only go down if you are going somewhere local, but cars do go quite quickly. Dd1's classmates have played out since they were in reception (though each has an older sib two years ahead). The houses are such that the mothers definitely aren't sitting with a cup of tea in the front garden watching them, mine and another front garden are sloping upwards with walls, no visability, and the other one is set back and on a slope. I should say that I feel both parents for me have let go too soon, sending a 4yr old to play unsupervised (although I probably wasn't much older when I did; but that was a long time ago!!!), but am curious as to when I should. One of them had another classmate round who was playing quite happily (though not sure his mother would approve).
Dd1 is now coming to the end of year 2(she is 7), dd2 is in reception. Neither of them are left unsupervised, they are both at the stage where they go into toilet cubicles etc without me and I wouldn't be watching them all the time at the park, but they don't play out, or go to the local shops, and I don't know when I would be happy for them to do that. They do brownies/rainbow, swimming and dancing, so we are fairly busy after school, when we are home it is usually homework, an imaginary game with them and ds(2.5), garden (when not waterladen), or cbbc.
Dd1 isn't particularly friends with these two children, and said she wouldn't want to (think she is shocked that they are out without their parents watching), but I know that she will need to learn to be more independent. It doesn't have to be playing with these children, who are a little wild, but just generally going out without me. She has a good sense of road safety and is quite sensible. Of course once she does, dd2 will want to too.