Question 749544
This is a factorial problem. 

6! = 6*5*4*3*2*1 = 720 different ways they can line up. A random lineup being correct is a 1 in 720 events. 

Note - This happens to be as simple as it looks, but there are situations choosing say 5 kids from a class of 20, which adds a layer of complexity. And whether those 5 are being chosen for 5 distinct slots (as in baseball) or 5 of the same type of position (say 5 extras in a play), the solutions become more complex.