Kids certainly spend more time and more money on video games than movies, primarily because video games last into the tens of hours (I myself have played skyrim on down times for a few hundred hours... especially when I'm sick). But this isn't to say that movies will disappear, or that games are mainstream entertainment. The difference with a movie is that it's designed for a mass audience. However, with a game it's really only yourself and a few selected friends. Film effect a culture as a whole with a very similar experience. But, my experience playing say, Skyrim will be different than yours because we didn't in fact interact and have the same game. Yes, the narrative is unchanged and fixed in a game, but the way in which we do it varies. In a more straightforward game, like say Call of Duty, it's more about the online play component which isn't narrative based in the way a film is. I can tell you about a cool match I may have had, but it doesn't mean much because you haven't seen the match, certainly not in the same way which I have.
This isn't to say that film interpretations for all people are the same, they are not, but they are really seeing the exact same shots in the same order, which is something you do not get with video games.
What perhaps is a more interesting comparison, as it competes on the same screen, is whether or not video games are really superseding TV. A movie is shown in a theater, normally, or with friends-- but there is an emphasis on a communal and broad interaction. However, with TV shows, you're often watching them on your own, in your house- much the same as when you're playing a video game. You can tell your friends about an episode you saw which they didn't but as with video games, since they didn't see what you saw, in a literal way, it would be a similar interaction. And when we speak of "main stream" we really are meaning culture as a whole, I assume, so this lack of direct ability to interact with what has been (seen or played in tv -v- video games) will probably have similar sociological responses.
There's my rumination on it now off for another coffee.