I think individual circumstances of the location, your relationship with neighbours, presence of a neighbourhood watch service, time of day when your daughter would play independently, how far away you'd be, and your child's maturity are all critical factors that are beyond the scope of knowledge of most of us here.

We live in a busy downtown area. For our local environment, free ranging at 6 would be beyond irresponsible. (Think: letting a child loose in Times Square.)

What is to give light must endure burning.