Place different people around the class (monitors or children).
On your signal, ask the other children to run to the people around the class and warn them of the coming of Jesus.
Explain how, in the Bible, Isaiah described the coming of Jesus.
You can do a relay race. Place the children in two rows. On your signal, the first child of each line must warn all the children of the coming of Jesus and return to the lineup so the next child can in turn warn the others.