Slice: Slice the top off each orange. We like to cut it in a zig-zag pattern to make it look more like the top of a carved pumpkin.
Scoop: Carefully cut around the inside of the orange to loosen the flesh, then scoop it out with a spoon. Set the orange flesh aside rather than throwing it away.
Carve: Use a small sharp knife to carefully carve a Jack-o'-lantern face into the orange peel.
Fill: Fill each orange with the blueberries, quartered grapes and any of the chopped orange you want to add back in.
Top: Replace the top and serve.
Notes
Choose oranges with a fairly flat base so they stand upright once filled.
A grapefruit spoon can make scooping the orange flesh out much easier.
Pat very juicy fruit dry before adding it so liquid doesn't collect in the bottom.
Keep the carved openings fairly small so the orange shell stays sturdy when filled.
If you're making a batch, draw several different face ideas on paper first so you can carve them quickly.
For young children, cut small round fruit such as grapes lengthways into quarters before serving.