As Ted said, most are content to pound nails into wood, but might do a project they can take home and enjoy. We always did either bird houses or cars. I typically cut out most of the parts and let them do the assembly (gluing, screws, nails, etc) and finish work (sanding, paint, etc.).
My son still has some old projects that he did from way back and he's not a sentimental type of person.
To a small child, the perfect granddad is unafraid of big dogs and fierce storms but absolutely terrified of the word “boo.” – Robert Brault