Always remember to share these wonderful little breakthroughs with parents after class. Share photos and a small writeup on what the children did, how they had to brainstorm and problem solve and what they came up with. The process is often more innovative than what the product shows - share it and make them proud!
Balloon, as thick as possible
Paper towel tube or 2 toilet rolls taped together
Tape or duct tape
Wine bottle cork
Skewer (if you want to punch holes on the sides of the tube)
Other bits and bobs that you have; wool, felt, foam sheets etc.