I think what a person perceives as safe depends on where they grew up. When my kids are nine there is no way I would let them take the subway alone but then again they aren't being raised in the city. More likely than not a kid who is raised in the city is a bit more street smart, knows all the rules about strangers/accepting rides and knows what areas to avoid. And to be perfectly honest, the "big scary city" isn't as dangerous as people think. The writer knows her child better than anyone else and if she is comfortable with giving him a little bit of independance then who are we to judge. If more parents stepped outside the bubble they've put their kids in they might just find out what intelligent, ingenious and self confidant kids they have.