Have several boys standing in a line (facing the audience) with one arm on the next boys shoulder.
The first boy in line looks at the second and asks the second boy, "Is it time yet?"
The second boy asks the third boy the same question and so on down the line.
The boy at the end of the line looks at his watch and says to the boy next to him, "No, its not time yet,"
and this continues on up the line to the first boy in the line again with each boy saying it in turn.
This can continue a couple times; then when it gets to the last boy, he says, "Yes it's time!"
When the message gets back to the first boy each boy moves his arm from the other's shoulder and puts his other arm on the boy next to him.
Variation: Everyone is sitting down instead of sitting up with their legs crossed the same way. When the time comes all they do is switch legs simultaneously.