Benjamin Franklin 'Hawkeye' Pierce was more voyeuristic and vicarious than most people gave him credit for. Sure he was crazy, the number of times Sydney had been called over because of him put paid to any doubt on that front. Sure he had a great record of keeping the kids alive that came through the 4077, the filing cabinets just outside Potter's office and the ones down with the number crunching idiots were a testimonial to the brilliance of ever doctor, nurse and core man in the outfit. Even Clinger's many different dresses had a file in Potter's records.
What wasn't on file was that when Trapper had left, Hawkeye had gone through his stuff before helping BJ settle in. What wasn't on file was that Trapper had left behind the letters and photos from his family back in San Francisco. What wasn't on file was that Hawkeye kept these letters in a tin beneath his bed, next to the tin that had the letters from his father.
He liked children, loved them really, and he wouldn't have minded having a few of his own if he weren't so terrified of the commitment that was required to actually get as far as making those adorable little bundles.
So he lived out parenthood vicariously through the letters that BJ read to him from Peg, and the letters that Trapper had left behind. He watched every other family that came through the camp and imagined that, if he had a family of his own, it would be something like that. He took nearly every child surgery that came through, wanting to hold onto the child and care for them, if only for a little while, and when Christmas time came around, and Father Mulcahy invited the sisters and the orphans over to bring some cheer, he was the first to volunteer to be Santa Claus.