At 3, he seems a little young to get much out of the exercise, and would likely require a lot of supervision to keep him safe from whatever hazards there might be, such as licking his wet hands after processing.
However, you could try letting him chose the objects and place them on the dry paper, then let him watch the processing.
As Jim says, as long as he is not trying to eat the stuff, there is no great hazard.
I was first introduced to this when I was maybe 8 as blueprint paper that my mother showed me and we made various photograms and such. Still a memory after all these years.
Last edited by bdial; 06-28-2012 at 02:03 PM. Click to view previous post history.