First of all, I am so flattered that you asked me of all people. You made my week, gorgeous ♡
It wasn’t easy, though, because apparently there is fuck all about Bucky before he joined the army. It’s like with Jesus, it’s like he didn’t exist during his childhood. But I’ve tried to make something coherent out of this mess of contradictions and vagueness that is Bucky’s backstory.
So let’s start with his date of birth. Ha. That’s easier said than done since — as agentbartomanoff pointed out — the MCU can’t even agree on which year he was born. This is a complete clusterfuck. But I will go with 1917, because I personally always have and it makes him just one year older than Steve.
Then we have month and date, which is hilarious considering the whole year snafu. But, in a deleted scene in The Avengers, Steve looks at the files of the Howling Commandos and SSR, and we get to see a glimpse of Bucky’s file.
Which is more or less useless, because it’s lifted directly from comics canon. It says he was born in 1922 in Indiana. No sir, that will not fly. However, we do see a partial date, which is 10.
So, so far, it seems Bucky was born on the 10th of some month in 1917. I have tried to find any reference to any month, but the only thing I could find were Bucky’s dogtags in this fantastic piece of fancreation which says May. The date says 20, but if we’re goingto cut&paste from everywhere, why not just steal bits?
So, in conclusion, if you ask me, I’d say that Bucky was born in New York on May 10th, 1917.
But this wasn’t the hard part, of course not. The hard part is that from here on, it’s a wasteland. We don’t even know anything about Bucky’s family. In an interview during CA:TFA Sebastian Stan said both Bucky and Steve were orphans, and the tie-in comic Captain America: First Vengence supports this. Then comes CA:TWS and suddenly Bucky is not only not dirt-poor but he also has two parents. Seriously, Marvel, you’re usually great at continuity, don’t drop the ball on us here.
I haven’t read the comics, but I am aware that in them, Bucky has a younger sister. And on the Smithsonian Board of Fail it says that he is oldest of four. I… don’t buy any of it. In the MCU, I mean. I have a younger brother whom I’m very close to and I love him to death. Bucky is very much a Protector, if on a smaller scale than Steve, and I can’t imagine him being any less devoted to his hypothetical siblings. So what is a clear indication to me that Bucky is an only child is how he says goodbye to Steve before he ships off. They both try so hard to keep it casual and light-hearted, but they still pretty much fail. But what is Bucky’s attempt? “Don’t do anything stupid ‘til I get back.” Which is a lovely line and I adore it, but if Bucky had had siblings, I guarantee you that he would have thrown in a “watch out for the brats/kids/[name]/etc” at the end. Because Steve is his closest friend and probably an unofficial part of the Barnes family, and Bucky would trust him with that responsibility.
It’s the same thing in the flashback in CA:TWS. Bucky only mentions that “my parents wanted to offer you a ride to the cemetary”. No mention of any siblings wanting to offer their condolences. When Bucky offers to “put cushions on the floor, like when we were young” there is again no mention of any siblings. There is a great big screaming void of No Other Children in the dialogue between Steve and Bucky.
So that is my argument for Bucky being an only child. As for his parents, I am at a complete loss. I’ve seen in some fics that Bucky’s father was a drunk, but I have no idea if this is fanon or has canon comics basis. The only thing that seems clear is that Bucky was middle-class. I have no idea how much this has to do with Bucky being healthy and having both parents alive while Steve needed tons of medicine and only had his mother. I don’t know enough about early-20th century America to make more solid guesses.
I have a personal fanon that Bucky’s parents were immegrants from Eastern Europe and changed their name to Barnes to fit in better. Which would also explain Bucky’s super-American name. But that is personal fanon I can’t argue for at all.
So, to recap: Bucky was born in New York on March 10th, 1917 to middle-class parents. He was an only child and semi-adopted Steve as His from an early age. He was good in school because he’s Smart and probably quite popular simply because he is Good With People. I also imagine that plenty of adults shook their heads and sighed that it was such a shame that Bucky chose to hung out with that little sweet-if-scrappy Steve Rogers.
I hope this helped a little bit, at least ♡