Whenever we paint, LM simply LOVES to paint an entire piece of paper in one color, edge to edge, corner to corner. So one time he painted a paper completely orange.
When it was dry, I drew a pumpkin shape on it and had him cut it out.
Then I drew eyes, nose and a mouth on black construction paper and had him cut those out too.
He glued them on, added a stem, and here is his Jack-o-Lantern!