1. Have the kids plant watermelon seeds to have them grow. Either plant in a cup with soil, or for a faster way of growing place a wet paper towel in a plastic baggy and place a seed in it, tape the baggy to your window for sun light. Keep paper towel wet, when the seed grows some roots and sprouts you can transfer it to some soil.
2. Cut a watermelon open and show the kids what and where the seeds are. What part can be eaten, and what shouldn’t be, etc.