When we start to teach children about meditation, we can help them become familiar with the process of observing their breath using games. Here is a simple game, in which we let children think of their belly as a balloon. While their mind is involved in the game, they actually end up learning to become conscious of their breath.
Of Course in Ana Pana Sati or Breath-awareness meditation, we allow the breath to flow without any manipulation such as emptying out our belly. But it is okay to use this game as an illustration.