We just got a fresh batch of screenshots and a new trailer for Super Mario Galaxy 2 which shows the green clad plumber having at it with the minions of Bowser. Sadly it doesn't look like Luigi and Mario will be a co-op pair that are playable in the game, as it's an either or scenario for your goomba stomping. You'll still be able to play co-op with the 2nd player controlling your sidekick star.
Still Super Mario Galaxy 2 is looking to shape up nicely, just like the previous game, and should be a great title to add to your kid friendly co-op collection.