you can also
grow different seeds. Lettuce, pea, green bean. Have them make predictions which will germinate first. Then have them use microscopes and be a scientist and document with illustrations. Don't tell them what each thing is yet. HAve them predict and guess. After you get roots and sprouts turn the cup or baggie they're growing in upside-down. Ask what happens and why.
I always have them start 3 sunflowers or pumpkin seeds to take home. They are thrilled and I've gotten a pumkkin from students returning in the fall!