If you want to know what a cyberpunk game is than look at the game and see if it fits with the question "How would todays world react to __________" if it doesn't than you don't have a cyberpunk game. I'm only brining this up because the creator of this thread put Mass Effect in as a cyberpunk...
No, you should be able to kill kids in video games. Everyone hates Bethesda for making it so you can't kill them and even in older Fallout titles you could beat kids to death in the crouch with a sledgehammer.
What RPG's have you played that include vehicles besides Fallout 2? Your idea fits more with Grand Theft Auto than an RPG game.
Edit: You shouldn't think of this as a Sandbox game but rather an open-world RPG.
Experience isn't given for being sucsseful in combat but rather experience is given for completing a quest or goal.
Edit: It could also work in a way which being sucsseful in persuading someone gives the same amount of experience that combat gives you when your victorious. A bad example of this...