I'm a command and conquer junkie. A few years back my then 5 yrs old son saw it and wanted it to play. (At this point he only played Reader Rabbit)
I set him up with a game with no enemies. He could build the base. He loved it. In fact to this day we still call it the 'building game'. I then set him up with a game with several other armies on the same team to give it more of a community feel. He could explore their base, etc. Then boy-i-fest destiny kicked in . He learned he could attack neutral buildings. Then he began to capture his allies buildings. Then he learned to bump (i.e., squash) his allies soldiers with his bulldozer.
So, bumping with bulldozers is how my son was yanked from the comfy world of Reader Rabbit games into the harsh, C&C-flavored lessons of imperialism and world domination