Needless to say, it is difficult to comprehend how sunlight, carbon dioxide, and water can make carbohydrates and oxygen. Cyanotypes provide one opportunity for children to get a hands on, sensorial, experience with a photo-reactive chemical process and the opportunity to achieve a better understanding of chemical pigments by analogy.
This is an incredibly simple lesson to set up and 2-6 year old children can make prints independently if you supply an hourglass or simple method for ensuring that the paper is exposed to adequate amounts of sunlight (we achieved good results with a 3 minute egg timer). Here is how the lesson looks on the shelf.
The children select natural artifacts, place them on the photosensitive paper, and wait until three minutes has passed. They seemed very interested in the color transformation of the paper; additionally, many found watching the sand pass through the hourglass to be an exciting point of interest.
I recommend supplementing the experience with an art appreciation lesson wherein you show the children some classic cyanotype prints; in particular, Anna Atkins, an English botanist and the first female photographer, has some very beautiful seaweed prints in her book Photographs of British Algae.
Older children can experiment with toning (changing the color of the print)- oolong tea works well! Also, here is something else that I plan to try (and present to the children if it is successful): http://www.alternativephotography.com/wp/processes/photsynthesis/photosynthesis-grow-your-own-photographic-supplies