For kids with the dexterity (and maturity) to handle small objects, bead crafts offer flexible options for both boys and girls. They're colorful and tactile, and beading projects typically go together fast, which keeps kids interested. Bead crafts can be refreshingly tidy, too, depending on the projects you choose.
Try having the materials on hand for three or four bead crafts, and let each guest choose his favorite. It's probably a good idea to assemble a few of the projects in advance as samples -- or have your older kids do it. That way you'll be able to provide a good visual as well as experienced guidance. We have a variety of how-tos to get you started, but your local craft store will likely have a good selection to choose from, too.