I've never played any of the previous Lego games, so I'm just wondering what type of Coop/multiplayer the previous games had. Are they online, or just split-screen limited to one box?
I don't know about the first Lego Indy or Batman but Lego SW: TCS did have online co-op. If you are playing online and you allow EVERYONE to join your game then they can just jump in in the middle of the game.