You can grow seeds in a jar, a carton or an egg box or even an egg shell! (You could also use grass seeds in the end of some tights to make a hairy funny head!)
Use mustard and cress to grow your own salad. 
Make the soil moist before putting the seeds on top. Children can use a spoon to water the seeds 
Sprinkle the seeds thinly 
Cover the seeds with a thin layer of soil 
Water regularly. Two weeks later you will have a nice crop.