Most breastfeeding how to books go at least a bit into why to as well as how to. But less and less, frankly, as the science becomes more and more incontrovertable and its assumed the "why tos" are a given.
I will think about books. In the meantime these articles may help?
Your grandchild is breastfed? http://www.llli.org/docs/00000000000...sbreastfed.pdf
Breastfeeding-it's just good sense:http://www.llli.org/docs/00000000000...tgoodsense.pdf
And I love this one from Canadian pediatrician and breastfeeding expert Jack Newman, who I think of as the cranky uncle of breastfeeding. He has a wonderful no nonsense style that is even more pronounced in person. If you ever get a chance to hear Newman lecture, take it. He's a hoot.
Breastfeed a toddler? Why on earth? http://www.nbci.ca/index.php?option=...tion&Itemid=17