Kids love to upcycle, they can look at something and imagine it as something entirely different. Letting them have stuff they’re allowed to demolish and make something new out of is fun.
I have had a few workshops with kids where I bring all sorts of garbage, broken toys, beads, jewelry and all sorts. Be sure to have tools, glue and such but keep it under supervision so they don’t go crazy with those chemicals. I have made a lot of mirrors with kids. It’s something that is easy to glue on and make look pretty almost regardless what you do. Mirrors can be found in abundance in charity shops. Just make sure before they start that you have a plan on how to hang it up, because they will want to display their art. Glue for mirrors can be bought at hardware stores, super glue will also work, but is more expensive. Making key chains and jewellery is also easy. The main thing here is to let the kids lead the way and help them achieve their goal.