Peel an apple and cut it vertically into 3/8-inch-thick slices. The slices need to be thick enough to stick a skewer through without breaking them. Using the small cookie cutter, cut out 20 stars and put them into the bowl of lemon juice, coating them on both sides.
Starting in the middle of the watermelon, cut it horizontally around the thickest part. From one-half of the watermelon, cut two large round slices about 1-inch thick. Try to cut the slices as evenly as possible so the stars are all the same size.
Using the smaller cookie cutter, cut 20 stars. Cut stars close together so you get as many as possible out of each slice.
Then use the mini cookie cutter to cut 20 small stars. Cut additional watermelon slices if needed.
Wash and dry the blueberries.
Add the fruit to the skewers in the following order: large watermelon star, small watermelon star, apple star, and 3-4 blueberries. Repeat for all the skewers.