Painting with wet chalk on black paper. turns the chalk neon and wont rub off! Fun way to do Rainbow Words! - fun, easy/simple, already have supplies (except need more black paper)
Maybe for Charlote's Web (?) Water color crayon resist artwork, an Original watercolour painting by Kirsten Bailey, but could be adapted for a children's art activity. Great for a fall wall hanging or spider picture for the fridge!
Group Mural Idea: start with black shapes - no touching - connect with lines - kids get one color - walk around and paint shapes - go over lines with black again for pop