Mask making is always fun. You can cut base shapes out of posterboard, then decorate with feathers, fabric, stickers, paint, etc.
Decorate cheap t-shirts. You can stamp paint on them, tie-dye, glue-batik.
Something with wet-felting -- balls, snakes, flowers.
Decorate pillowcases with fabric markers -- always a good sleepover craft.
Family Fun magazine usually has lots of ideas for a big age span. I think their website is
www.familyfun.com. This month's issue has crafts like using the plastic from deli containers as a paint canvas, using a reverse paint technique (layering the paint so that the finished design is viewed through the plastic), making old plastic bottles into dolls by wrapping them with string and using wooden spoons for heads, making balancing sticks (which look like fairy wands...also includes ideas for using them, like balancing them through an obstacle course), making a faux fishtank out of an empty bottle (I really want to do this one with my 4yo), making a crocodile out of watermelon (okay, not a good craft for your sleepover, but I think it's hilarious). Our library has Family Fun issues for check out, but most of the older issues are online.
Ooo, also, maybe doing some astronomy-type crafts would be fun?
Really, the big problem is too many choices, lol.