Give each six a postcard and see if they can get themselves through it
plenty of postcards
give each six a postcard and ask them to make it so they can fit themselves through it. Have plenty of spares for any mistakes.
Explain that the postcard must be intact (so no cutting it into pieces) and that each member must fit through it (one at a time).
There are more activities on the pdf - but simple instructions on how to complete this.