Wet on wet watercolor painting is fun for all ages. This process is an art staple in my home with children under 6. You can find all the recommended supplies on the supplies page of this site. You can use food dye and spill proof cups in place of stockmar paints for the littlest painters, or for a budget friendly option.
My two artists love Wet on Wet Watercolor painting. I’m sure yours will as well. Have fun!