This is a fantastic exercise! I love it. This part especially, including them in transparent conversation, building awareness of what they're doing:

Ask them if they were aware that they just controlled their body’s actions, that they used their minds to stop themselves from doing something they really wanted to do. Tell them that this is called having self-control!

Encouraging children to meditate is a wonderful thing too. We haven't done much, but hoping to make it a regular practice with our kids at some point. We just cleared a room in our house to make a meditation/yoga room. Creating space and awareness is a good first step. ;)