Some great instrument making resources that you may want to check out: Sound Designs by Reinhold Banek & Jon Scoville & Musical Instrument Design by Bart Hopkin (this is the best reference book on instrument design I¢ve ever seen). Also, check out http://windworld.com/, this is the home of the infamous magazine Experimental Musical Instruments. Bart Hopkins runs the page and he¢s got some great resources available and you can get a CD-ROM (or photocopies) of all the magazines. I seem to recall a few great articles on teachers working with children creating homemade and found sound instruments.
You might want to check out the Kennedy Center site for ideas/lessons, http://artsedge.kennedy-center.org/.
Hope this helps!