To answer Prof. Kleiman's question, the last (and heretofore only) child of a President who was eligible to serve in the Armed Forces at a time of war, but failed to do so was...John Payne Todd, step-son of James Madison. Very interesting character, that Mr. Todd. He was the only surviving son of Dolley Madison from her first marriage, and was still a toddler when his mother met the future President in 1794 (at the time, Todd's guardian was a friend and political ally of Madison's named Aaron Burr). When the War of 1812 started, he had just turned 20.

He seems to have been spoiled by his mother, and spent much of his early years at school, far away from the political world his parents occupied. He quickly gathered some worrisome vices, including a proclivity for drinking and gambling that would, over the fullness of time, bankrupt his widowed mother. Rather than putting the boy in harm's way, at a time when the British were sacking the White House, his step-father sent him on a diplomatic mission to Europe in 1813. By all accounts, he embarrassed himself on the junket with his public drunkenness, and the nation remained at war for two more years.

In short, nothing at all like the current situation....