This game is derived from the popular backyard game that of course uses mallets, wickets, and stakes.
In the soccer version, the wickets (or gates) are made up of two discs or cones space a couple feet apart. Spread these out in a "course" with distances appropriate for your age range and field size, ideally with obvious starting and ending gates. Obviously the further apart your "wickets" are, the more challenging the game is.
One way of doing this is to send your first player off, then the second when the first player makes it through the first gate, etc. Or, you can set them up in small groups more similar to real croquet, with 2-3 players aiming for the first gate at once, even allowing lost turns if one player makes a pass and hits another player's ball.
Be careful that you don't create a line with players waiting idle at the end. With lots of discs/cones you can have several courses going at once so everyone stays active.
Stress solid passing technique during this drill. It's excellent for practicing ball speed and accuracy.