On Going Outside the Yard

Two posts back I mentioned that our children "don't go out the yard much" as it's too risky.  I got two questions about that.
Firstly, I meant 'out of the yard' not 'out in the yard', and secondly, as a sort of disclaimer - not all parts of South Africa have these problems. 
Our older children very, very rarely go out of the yard by themselves.  The younger ones - NEVER!
The first reason is that some people seem to forget that the speed limit in a residential area is 60km/h.  They race past our house at well over 80, and that's way too fast to stop in a hurry.  Sometimes, on a Saturday or Sunday afternoon, Malcolm or I (or both) will go and stand outside with the kids while they ride their bikes up and down in front of our house. 
Which is not very exciting for the older ones...
The other, and bigger reason is simply the crime.
There is far too much risk of being mugged, having your bike stolen (at knife-point - or worse), children being kidnapped, girls being raped etc etc to allow our children out on their own.  And no... it's not to say that those things will happen, it's just that there's a very high risk that it could happen.  And which decent mother is going to take that chance??  None that I know of around here.
My nephew was held up at knife-point a few years ago, while on his way home from school (he was walking).  He was forced to empty his school bag, and his cellphone, calculator and money were taken.  This happened on a busy street!  Nobody stopped to help him!!
Down the road from our house, about 3 blocks away, stands an old disused quarry.  It's got a lot of trees growing around a small dam in the middle.  When we moved here, it was the potential site of an upmarket security village, built around the dam.  In 6 years nothing has happened, the developer probably ran out of money.
In the last two years, it has become a home to many vagrants and illegal immigrants from neighbouring countries.  During the day they wander the streets.
In front of our house is a 'park' - an open piece of grass, with a slide and some swings.  Guess where all those vagrants like to sit???
In front of our house!
They lie and watch our every move.
They use the trees as toilets.
They leave rubbish all over, despite the fact that there are bins.
They like to get drunk over the weekends.
They are loud.
And we can do nothing about it!
And the police won't can't either.

Would you allow your children out?