Through nature to eternity: The bog bodies of northwest Europe by Wijnand van der Sanden (Amsterdam: Batavian Lion International, 1996)--The best book about bog bodies (written for adults by an archaeologist from the Netherlands) and (to my knowledge) available only from the Netherlands. It has hundreds of pictures, covering almost every bog body ever photographed, even those destroyed during World War II. It also contains the latest archaeological and scientific information  on the study of bog bodies. If you are writing a term paper on the subject, this is the most invaluable resource you will ever find. 

Occasionally, you can find a used copy available on Amazon. Follow these links to check for hardcover or softcover .