I've just posted a craft project to make spider webs. Almost any children can do this project, but the younger ones will need some help with the web portion.
If you are working with a group of younger children, try adapting the project to make it simpler for them to do it on their own. Skip winding the thread around the arms of the web. Instead, use the idea of pulling apart bits from a cotton ball. They could use glue to attach the cotton wisps to the arms of the web.