Choose teams of 10 to 20 children and get them to form separate circles.  On your word, they must close ranks to form a huddle.  Then instruct them to close their eyes and hold up their arms.  With their eye still closed (they must not cheat!) they randomly join hands with other kids.

Then tell the children to open their eyes and attempt to unravel the "knot" without letting go of anybody's hands.  Award small prizes to the winning team.  At this stage the teams have thoroughly bonded, so you can then use them for other activities and games.

Have fun!