Scratch art is a very easy and fun technique that we can try with kids 3-5 age group. It is a good mix of open ended + technique driven art elements.
Few points to consider:
- small note size thick paper
- tape the paper
- Oil pastels
- thin layer of black paint would do
- have something sturdy, and pointy for scratching the paper like a pencil, fork, stick
Here are some pictures.