How do you unlock all worlds on new Super Mario Brothers?

World 2: Beat World 1.

World 3: Beat World 2.

World 4: Beat the boss in the castle in World 2 with Mini Mushroom.

World 5: Beat World 4 or 3.

World 6: Beat World 5.

World 7: Beat the boss in the castle in World 5 with Mini Mushroom.

World 8: Beat World 7 or 6.