Or do some movement and singing activities to try to release all their energies. Maybe do a short outside time to let them run, if possible. Tell a VERY animated story. Children will start singing too and it gets quieter. You can even sing quieter as more join you.
Some people have a signal like a hand in the air or turn off the lights.
A whistle might be used to signal quiet depending on your program. Some people speak in a quiet voice. The children want to know what is being said, so they get quiet. My children always sing with me. Try to redirect the child to an acceptable behavior.