I’m 32, and my dh who is 30 doesn’t remember doing any of these.
Cress eggs. (Doing these with the children tomorrow). This is where you get an egg shell, draw a face on it, sow some cress seeds inside, the and the egg grows “hair”.
Grass “potatoes”. You get some tights, stuff it with grass seeds, give it a nose and eyes, and the hair grows upwards giving them a funny expression.
Bean seed in a bottle. Get a plastic bottle and line with some paper towel. Put the bean seed in between the towel and the plastic so it’s visible. You can then see the root and the plant growing.