Just to prove I'm not all about the yarn craft, here is a simple thing we did at Master Four's recent birthday party. I wanted to have something open-ended, that could be dragged out to last a while, and that kids could jump into at any time, as an ice breaker, and also while waiting to see if anyone else was going to turn up (don't you just hate non-RSVPers?) This was fairly simple to set up, and mostly done before time too.

I cut out circles of cardboard, edged them with silver duct tape. That's it. Oh, well, I also cut out handle sized strips of cardboard, and taped along the longs sides of each, so they would be smooth for four year old hands to hold. Then I furnished the room of children with crayons and pencils, and let them draw their emblems on the blank side. (The one pictured above is Miss Six's Toothless shield, isn't she a great artist for a little kid?)
Then I taped a handle to the back. That way the young'uns could draw freely without their shields wobbling all over the place. Best part - it was all free, from the giant crayon collection my three kids have, to the cardboard from the sides of nappy boxes, to the duct tape I already had. And boy, did the kids love them!