Papercraft (you print out 10 pieces of paper, bring scissors, glue, let them have at it usually does 2 things -- they're interested in a build and are learning build skills and they're keeping quiet.
A few for you to look at:
robots:
http://members.chello.nl/m.egtberts2/pdf/retrobot.pdf
Color their own/make their own:
http://members.chello.nl/m.egtberts2/pdf/fs_blank.pdfhttp://thunderpanda.com/509/
Thunderpanda Troops:
http://thunderpanda.com/509/
