There's very little risk of your son being a victim of violent crime, if that's what you're concerned about. Scammers are unlikely to target an obvious child, foreign or not, as most are generally smart enough to realise that he/she probably isn't carrying much money. As for being paranoid about carrying around an smartphone/iPod, spending ten minutes in any Chinese city would make clear to you that nearly everyone is openly walking around with one of these things and yet somehow not having them constantly plucked out of their hands.

As others have said, the biggest risk is in being run over by a lorry or picking up some stomach bug from street food. Assuming you trust the guide, I see nothing to be concerned about.