Begin by teaching the preschoolers that each flower has five basic parts. These parts are the roots, stems, leaves, petals and seeds. Explain that the roots are found below the soil, and that they are responsible for drawing up the water and nutrients the flower needs to survive. The water and nutrients are then carried through the flower's stem to be delivered to the rest of the flower parts. The plant's leaves absorb the sunlight to turn the water and nutrients into food for the flower. Finally, the petals surround and hold the flower's seeds. The seeds are needed to create new flowers in the future. Preschools are not ready to learn the more detailed parts of a flower, such as the stamen and pistil.
Take a field trip to a field of wildflowers, or bring in one potted flower for each child to dissect. Go through each of the flower parts one at a time. The preschoolers will need to dig around the base of the flower to pull the flower out with the roots still attached. Give each of the students a magnifying glass to observe the roots up close. Cut the roots away from the stem with a pair of safety scissors. Instruct the children to observe the end of the stem with the magnifying glass. Next, have the preschoolers pick apart the leaves and petals of the flower to be observed under the magnifying glass. Finally, let the children blow on the seeds, or disturb them with their fingers to show them how the seeds are dispersed. Remind the students that these seeds may travel via wind, bees or on the backs of some other animals where they will settle in a new place to grow more flowers.
Reinforce the parts of a flower by incorporating some activities into the lesson plan. You can cut the plant parts out of construction paper and give each student a chance to put the flower together. You can also draw a flower on the board and call the preschoolers up one at a time. Yell out a part to each student, giving him time to point to the correct part of the flower. Then ask him to reveal what that flower part's function is. Repeat until you are confident the students understand each flower part's location and job.
Give each preschooler a home-and-garden magazine. Tell them to cut out the five different parts of a flower from various flowers throughout the magazine. Then, ask the students to create a flower by gluing those five parts together appropriately on a sheet of construction paper. Another flower part craft you may choose to use involves clay. Give each child a set of modeling clay and require them to create a flower with all five part. The colors they choose to use are not important as long as all five flower parts are correctly identified.