You will need your favorite fruit, preferably big things like watermelon and whole pineapple, as well as smaller fruit like cantaloupe, honeydew, kiwi, strawberries, grapes, and any other fruit your kids love or you just happen to have around the house. For the stems, use small bamboo skewers.
I have a flower-shaped cookie cutter that we used to cut out flower shapes. The kiwis I just sliced and for round centers, I used a melon baller to create half spheres or hemispheres. The cantaloupe I cut into wedges and used those for leaves; honeydew would work great, too. This is a great project to let your kids experiment with their flower creations.