I read somewhere that they had all just returned from a parents' evening at school about 10 minutes earlier.
It looks like a very quiet estate, there were other children with her. It doesn't sound beyond the realms of 'safe' to me at all.
And bad things happen to children who are in 'safe' environments - depending on who is around and decides to do something disruptive.
I don't think these poor parents did ANYthing wrong, and yes I have a 5yo myself, and I don't live somewhere that it would be very safe to let him out at 7pm but from the looks of it they made a rational and competent decision and it wasn't their fault anything went wrong 