The children sit in a circle and close their eyes. Then, the person running the activity walks around and taps one person on the shoulder. The person that got tapped leaves the room or hides somewhere where no one can see them. Everyone opens their eyes and tries to find out who is missing. To make it harder, have them stand up and move them around so they don't know who is near them.
Requirements
A space that is big enough to fit the group and a spot for someone to hide.