Totally serious Thunderbolts theory:
Sam's busy finding people to add to the Avengers roster while Bucky is being paired up with a team of delinquents, some who mean well more than others.
So in between that and running for fucking Congress, Bucky just calls Sam up like "babe I know you're busy and all but we're so not qualified for this shit pls help" and Sam's so unbothered, laughing over the phone, and is just "good luck babe, kiss kiss, bye." And hangs up.
And Bucky's like "fuck I can't be here" and full mentally checks out going Winter Soldier mode because between Alexei "Red Human Disaster" and John "Gaslight, Guilt Complex Agent" Walker, he hasn't had enough therapy to handle them let alone a bunch of traumatized feral super powered women.
But by the end he adopts them all anyway and then he comes home like "Sam we have kids now, no I know one of them is older than you and the other one is Walker, I don't care they're ours now" and Sam just has to except that they're parents now.
Then Joaquin shows up the next day in a cardboard box that has the words "free puppies" written on it, and Sam tells Bucky they have one more kid to add to their collection.
