NADA..absolutely nothing and really, if having the 3rd or 4th most successfu movie of all time can't get people to read Batman in higher numbers, they are screwed..
Kids aren't buying comic books for two reasons:
1. Availability. Comic books are generally only sold in specialty comic book stores, not normal sales channels kids know about. When Billy Everykid goes to see Iron Man and The Dark Knight and thinks that Batman and Iron Man are really cool, he goes off to Wal-Mart and Toys R Us, or Target, or Meijer, or other big stores and buys DVD's and action figures and other toys. When he's going through all this, comic books aren't there. To get comic books you have to drive to a comic-book specialty store, one that isn't part of a big chain and doesn't get instant name recognition and probably isn't advertising very much if at all. You'll find some graphic novels at the big bookstores, but it blends in with the crowd there of of the other superhero media like novels, video game guidebooks and other movie tie-ins.
When I was a little boy, in the early 1980's, I remember seeing some comic books in the magazine racks of convenience stores (that's where I bought my G.I. Joe comics as a kid), but that didn't last for long and a few years later I had no real clue where to go to get comic books.
2. Pricing. Comic books have gone way, way up in price. Comic books used to be petty, pocket-change things because they were on pulp paper with four-color graphics and meant to be enjoyed by kids. Now they tend to be "graphic novels" on glossy paper with fancy graphics, and prices that eat up a lot more of a kids allowance proportionally. Emphasis on intricate continuity and long story arcs now also makes it a lot harder to just jump in and read one comic book and get a complete story. The things that made comic books more mature and appealing to the more mature audience has ensured that they will be read mainly by the dedicated adult comic book collector.
As for how this relates to RPGs, it's pretty much the same. Kids nowadays aren't going to just pick up D&D at Wal-Mart or Toys R Us. When I was a pre-teen in the early 90's I picked up my very first D&D set at Toys R Us, the 1991 "Black Box" Basic D&D set, but I was just in my local Toys R Us yesterday shopping for my 4-year-old's birthday and was curious, and there is no version of D&D for sale there that I could find. Ditto for Wal-Mart, Target, Meijer and all the similar big chain stores, and ditto for being available at big bookstores but that's only one relatively small avenue of distribution.
Also, what is the entry cost for D&D now? Aside from simplified beginner sets that really aren't meant to be long-term play solutions, starting to play D&D involves buying (at least) a PHB, MM, and DMG, as well as dice, and probably miniatures (which if you're using official D&D minis turns into the whole collectable issue and prices involved), so you're probably looking at $120 or so (at least, before suppliments), which for a kid isn't exactly cheap. I will admit that the last intro D&D set I looked at was the 3e intro set released in late 2000/early 2001 which was definitely not a long-term game as it had 1st level pre-gens of a few of the 3e iconics with no customization or advancement rules and was very simplified. A product which includes D&D rules for creating characters of at least a few races and classes from 1st through some low level such as 5th and a balanced but small list of monsters and magic items would be a good solid intro that would lead into later products but not be so crippled as to only be somewhat playable by itself.