What you need:
Pair of scissors
This can be done like a magic trick, pick up the postcard and ask if it's possible to step through it, of course, everyone will say no!
Fold the card in half lengthways, then make cuts from the folded edge, stopping about 1cm from the edge of the card, each cut should be about 1cm apart.
Then turn the card around and repeat from the other side, so you are cutting between the cuts you have already made. Open the card out again.
Now, be careful, you don't want to cut from the very edge, so put your scissors over the very first (edge) strip then cut through the centre, be careful not to cut the last strip (the other edge) too.
You will end up with a piece of card looking like this...
Carefully open it out, it will be a big hoop of card and then step into the middle.
Pull it over your body....
Steady as you put your arms through....
And taa-daa, take a bow and collect your winnings - assuming you have taught your child how to place bets!