Standing in lines in their sixes (at least 4 lines) each line is given a # when the leader calls out a number that has thier number twice i.e. #22 then the second line all does a bop. If #21 is callled then #2 and #1 swap places and now have new numbers.
Have at least 4 lines, the lines are the numbers not the children. When a number is called that is thier number twice i.e. 11 22 33 44. Then that line does a bop. If a number is called that has their number in they then swap lines with that other number i.e. 12/21 then lien one and two would swap places. Now the children that were in line two have become line one and vise versa. A person is out if they bop at the wrong time, don;t bop, too slow or are last to get to the new spot.