Ahhh...I was a Girl Scout for 7 years and an elementary school teacher after that; I know crafts!
It's close to Christmastime, so if the girls celebrate, here's a crafty way to make ornaments:
1. Get a jigsaw puzzle and have the girls paint it green with tempera paint (or paint it yourself and let dry first if you're worried about messes
2. Give children old Xmas cards they can cut pictures out of, circular, approx. 3in in diameter. Provide circular stencils and pencils because children at this age can be easily frustrated trying to draw a circle.
3. Glue painted puzzle pieces around the circle, in a couple of layers. If there is enough adult supervision use hot glue guns, if not, paste.
4. Use ribbon to glue a bow to the top or bottom
Result looks like a wreath around the picture, and they turn out super cute.
Next up, the fabulousness of Mod Podge:
1. Get a shit ton of glitter
2. Get Mod Podge, mix with glitter
3. Paint things with your new glitter Podge! Great for decorating pendants for necklaces, canvass (they could do tote bags, coin purses, pillows, sneakers, etc), picture frames, and so on
Paint tee shirts:
1. A bunch of plain little girls' tees will be cheap, you could probably buy an 8 pack at KMart for $12.
2. Provide stencils and sponges and let girls paint away. Normal acrylic paint will do, though you can also find special fabric paint at an arts and crafts store.
Some other ideas:
-macrame friendship bracelets