I did quilting with K-5 for a summer at different "camps" at the schools in Charlotte. I'm thinking that in a days time and all those grade levels, you are only going to have a few minutes with each age group. I would go with making paper quilts with your little ones. Construction paper and glue and their good. I used one of those paper cutter machines like the Accuquilt does for cloth. Cut out all kind of different shapes that the kids taped down.
With the 2-3 we did stitching on burlap. Most of them stitched their names
4-6 did little blocks from a panel of blocks
When I taught my friends daughters they were in the 6th & 8th. We started with crazy quilt blocks. Mistakes were easy to cover, lol
Sounds like a fun day. I would dress up!