OK, well the latest HD4000 graphics found in many notebooks is pretty good. But I've got a feeling that Wow may lead to more gaming in the future (year or so). Now, I understand he's only ten, and when I was ten, my attention span to a new game or something (and this is back in the DOS days by the way) was about a few weeks, then I'd be onto the next latest game. I can remember back around that time when a 486 was the best proc to have....
I will agree that the Intel HD has been pretty good, as long as it's at least the HD3000, but one with dedicated graphics is maybe only 10% or 20% more than one without from what I've seen. And especially if one is ordered now, you may be able to get such discounts so that normally it would be as cheap as one with only integrated graphics.
I don't play Wow and never probably will (not into those types of games, honestly), but keep in mind that onboard graphics on laptops differs greatly from the desktop equivalants. So I guess I would say to get one that you can return within 30 days if the onboard graphics is not up to the task. At 10 years old, he may not be as concerned with the oddities of onboard graphics as those who are obsessed with frame-rates and the higher-end stuff.
So to the original poster, the HD4000-series would be fine (and maybe HD3000 series) but probably nothing less. I've just had bad luck with Intel HD graphics, but the newer chipsets are worth the consideration I guess. From my experience, the Intel HD chips are good for average users. Anyone dealing with graphics, video, or whatever, should avoid them. With Games it can be a mixed bag. The system requirements do require something like an 8600GT mobile or better, which the HD graphics may exceed.
BTW- For $600, you can probably find a good customized Lenovo or Dell. With Lenovo, you are paying a bit extra for the brand and durability (most of their laptops are meant for the traveling professional). With Dell, you can maybe get a little more for the same amount of money. They tend to offer more gaming graphics cards too, whereas all I've seen from Lenovo other than Intel HD is the Nvidia NVS Quadro.