This is a "commissioned" project I did a few years ago. A woman asked me to paint American flags on some pumpkins, and they turned out pretty well. She used them to decorate her porch, and the next year she asked me to do more.
It was a very easy procedure. I scrubbed the pumpkins with a vegetable brush, then transferred the designs using tracing paper and graphite paper. I painted the designs in bottled acrylic paints. When it was dry, I finished with a clear acrylic top coat to help it last longer.
Of course, it's a temporary thing, since the pumpkins will eventually rot. But so much fun! Of course, you could use any design. I think kids would love to see these painted with their favorite characters.