A pencil with a rubber on the end
Some chalk or pebbles labelled N,W, E and S
You will need to:
Cut a small slit into each end of your straw.
Cut out an arrow head an tail from your card.
Attach the arrow head and tail into the slits on each end of the straw.
Take your plasticine and squash it into the bottom of your pot (it needs to be deep enough to support the pencil)
Place the pencil into the plasticine (rubber end up)
Use the pin to attach the straw arrow (at the middle) to the rubber, make sure the straw can move with the wind.
Use a compass (most smart phones have one now) to find North. Place your pebble or mark on the ground with the chalk. Fill in E,S and W.
Get your children to keep a diary of wind direction, you could also use this to help them learn and record details about the weather and seasons.