Designate one child as the leader. All of the players should get in a straight line, kneeling down with their hands over their head. Make sure to designate a new leader each game, as to not single anyone out.
Have the leader of the game place his or her hands on the back of the first person kneeling down. The leader will then use the first person's back as leverage to leap over the first person. The leader will jump over the first person in line with his legs apart, just like a frog.
Have the leader continue to jump over every person in line in the same fashion until he reaches the head of the line. The person in the back of the line will then jump over everyone in the line until they reach the front.
Repeat this process as many times as you like, as a game of leapfrog can go on indefinitely. There are no winners and losers, just make believe frogs having a great time.