The group each takes a piece of a picture, colours/paints it themselves, and then the pieces put together make 1 big, multi-coloured image. You could do this for a card from your section, or just a commemorative art piece - for example, we're doing a giant version of the NE Regions '30th Birthday of Beavers' badge.
Large card, sharpie pens (or similar, for drawing the image outline), pens/pencils/crayons/paint/collage materials
For younger groups, the Leader should draw the image onto large card and cut it into the right number of pieces for everyone to have 1 each, before the session. For older groups, they might like to work together to build up a picture of their own.
Once the image is drawn onto the card & cut into the right number of (equal) pieces, each member of the group colours their own piece in. Let them be creative! You might like them to write their name on the back, too.
As the group finish colouring, have a grown up stood with another large piece of card (we actually use foam board for this), sticking the pieces together in the right order to build up the whole picture. Those who have finished can then watch as the picture comes together.