I fired off a letter to the editors of the "grandparents" column. Here it is,
for anyone interested:

Dear Dee and Tom Hardie, fellow Grandparents,

Your advice to the grandparents of the breastfed 10-month old was completely
out of line. Breastfeeding is so important to the health of the mother and
baby that several states have introduced legislation to protect the mother’s
right to breastfeed in public, whether or not her breast is exposed in the
course of nurturing her baby. The young mother should be commended for
continuing to breastfeed her "thriving" son, discretely or indiscretely,  in
the face of humiliating discrimination from those who apparently share your
beliefs.

Enclosed are copies of the Florida and New York laws for your information.
 New York’s law is even stronger, declaring breastfeeding a civil right, and
imposing penalties for anyone who attempts to discriminate against the
breastfeeding mother’s right to nurture her child appropriately.

Please publish a retraction of your old-fashioned, inappropriate response and
join Surgeon General C. Everett Koop and health agencies worldwide in
establishing "breastfeeding as the community norm."

Sincerely,
Linda J. Smith
Grandmother of Carrie, age 4
Dayton, OH