One of the most engaging ways to help kids learn about plant growth is to let them grow their own seeds over the course of the unit. Label plastic cups with the students' names and find a sunny space near a window to line them up. Let each child put a few inches of potting soil into his cup and plant a few flower seeds or pre-soaked beans. Help the kids keep their plants watered and observe the growth process together over the next few weeks.
Bring plants into the classroom in transparent containers that show the roots, to offer a very concrete demonstration of leaves, roots, stem and petals. Children may also enjoy creating construction paper plants by cutting out different plant parts and gluing them onto a sheet of paper in the right positions. Another approach is to go outside and observe different plants near your school or home, pointing out the parts of the trees, bushes and flowers you find.
Help each child trace her hand on a sheet of colorful construction paper and cut out the shape she traced. Wrap the cutout in a rough circle so that the parts below the pinkie and thumb touch and tape or staple them together to form the crown of the flower. Glue on a green construction paper strip as a stem, green paper leaves and a tan or white hand print cutout as roots. Fold strips of masking tape in half to create tabs and stick the ends of one tab to each component of the flower so that kids can label the parts as a review.
After your class has a basic grasp of the different parts of a plant, you can teach them about the edible parts of various food plants. Bring in a variety of fruits, vegetables and legumes such as celery, carrots, peas (in the pod if possible), potatoes, berries, zucchini, lemons, peanuts, spinach and lettuce. Explain that we eat different parts of different plants. Show that celery is a stalk, carrots are roots and peas are seeds. Kids may also have fun guessing what part of a plant each food is once they get the idea.