Sounds like some paranoid parenting that seems to be in style right now. In Tokyo kids take the subway by themselves as young as age 9. In denser cities the density helps in that other people help socialize/watch your kids and they can bike around to their friends place when they are older. As someone who grew up in a denser area, then moved to a sprawly suburb where you were dependent on your parents for getting you around, and lack of public space made activities revolve around consumerism, I greatly preferred the dense area.