Ideas
Here are instructions to a retractable telescope (not real, made from cardboard tubes) for kids. Looks like a lengthy, but not too difficult assembly. Might have them ready to assemble and decorate, or partially assembled before class. Certainly a younger to middle elementary idea.
http://www.piikeastreet.com/2012/06/telescope/
For the older kids, you might try making a periscope. Here are some thorough instructions designed for a working with a group of kids.
http://www.sciencetoymaker.org/periscope/assembl.html
It would be fairly easy to make miniature door knockers out of dangle-type earrings. But not much for the kids to do. However, if you had classroom Bibles (or the kids' personal Bibles if parents didn't mind), you COULD make knockers for their Bibles. Brainstorming here, but perhaps you could make foam ones and incorporate it in a Bible cover of some kind.
Perhaps a sign for the kids' doors would work. The kind that hang from their door knob. You can get nice ones made of wood that the kids could sand and paint and/or mod podge the verse on them, too.
Staci