It's the one with the visiting doctor and Hawkeye's birthday, which he gets out of by going with the surgeon, against his will, to a battalion aid station, to attend to a surgeon who drove his jeep into a landmine and was too unstable to move for help. At the end of the episode, a group of soldiers wonder in from the front, almost frozen to death.

The older surgeon is DEF his dad, but who is the kid who wonders in from the front, frozen? Brother, son, cousin?

I found the following info online:

"Antony Alda (born December 9, 1956, France as Antonio D'Abruzzo) is a French-born television actor who is the son of Robert Alda and half-brother of Alan Alda."

http://www.imdb.com/name/nm0017372/bio

Antony was in the Season 8 episode you've described with dad Robert Alda, who also appeared in a Season 3 episode.

gotcha, thanks very much!

The episode was "LEND A HAND" and I think it's from season 8. The other one, with his Dad, is "THE CONSULTANT" from season 3.