First, an obligatory comment about how useless this is without seeing the actual article: from the description here, this sounds like a completely contrived study designed (consciously or no) to support a preconceived idea of how children are affected by games. No actual measures are described and it smacks of pop psychology.
Children are very plastic in some ways, but they're also much more sophisticated than we often give them credit for. Typically, moral learning (and almost any other learning) is contextualized even in kids. It's worth noting that contextual leading almost always bleeds over somewhat, so I wouldn't be surprised if there is an effect, but it's likely a pretty small one. Kids pick up on the difference between games and reality extremely quickly and contextualize learning and behaviour very naturally (this is how brains work, it isn't something the kid needs to make a conscious effort to do, just as you don't need to constantly tell yourself that real life isn't GTA4).
Also, let's be honest here: "Communication Professor" does not inspire the most robust level of confidence.
Addendum: This is hardly any parent's fault. Morality isn't some magic little set of switches in the brain that just get set to one setting and can never be changed. Parents can't really indoctrinate their kids such that further moral development is impossible, so good parenting doesn't make kids "immune" to this somehow. Hell, even though you can contextualize it perhaps even better than kids (which is still a matter of active debate), you are affected by playing violent games absolutely guaranteed.
It's also pretty ludicrous to blame parents for buying inappropriate games for kids when the rating system is so wonky (and awkwardly conservative for a lot of American parents, which lumps acceptable M games in with things kids shouldn't play), the sales protection is relatively easy to bypass, and some marketing departments are going out of their way to make their target audience ambiguous (I'm looking at you Dead Space 2). Sadly, I'm not really sure how you manage to fix this. Movies have it easy because it's a small enough time investment and prerequisite level of experience that it's not uncommon for parents to go to movies with their kids, but that's just not a model games can really use.
