Thor
Thor is not an Alpha, he is not a Beta or Omega either but Bucky knows he is still theirs, that the Alien/God, whatever, has been adopted just the same as all of the other Avengers.
Thor is loud, boisterous and probably older than Bucky could ever hope to be and yet Bucky finds himself standing here, glaring at the Alien that had intended to ruin his dinner by gorging himself on poptarts.
"No, Steve spent all afternoon making dinner." Bucky growled out.
The man opened his mouth, most likely to protest that he'd still be able to eat the meal but Bucky was tired and he was not in the mood to negotiate poptarts before dinner.
"I'll allow one package for after dinner but not before, you guys are ridiculous, it's like you've never had parents to tell you no." Bucky said, exasperated.
None of the children listened, except for Hulk, he was an absolute sweetheart when he wasn't frightened or protecting Bruce. It was exhausting, even with Steve's help, Bucky couldn't imagine doing this parenting thing without the Omega, that would be a sad disaster.
"I am a prince of Asgard." Thor thundered.
"This is Earth, buddy." Bucky sighed, "If you don't listen then...then..." Bucky trailed off trying to find a reasonable punishment for a literal God other than grounding him, "I'll tell Steve to stop buying poptarts at all."
"You would not dare." Thor yelled but he sounded unsure.
"Try me." Bucky growled out.
"I believe that Sargent Barnes is rather serious, Prince Thor." J.A.R.V.I.S. intoned from above, "Last week he locked Sir out of his lab for not going to bed before the midnight hour."
Bucky pointed to the roof as Thor stared at him.
"Listen to the nice A.I., you can have one package of poptarts for dessert plus whatever Steve made for dessert and I don't want to hear another word about it."
Thor grumbled but subsided, wandering off, probably to complain to his lady love about Bucky taking away his poptarts or to see if she had any squirreled away.
She did not as Bucky had removed them from the lab and forbidden the young lab assistant Darcy from being an enabler, going so far as to sneak up on her to take whatever unhealthy snack she'd been about to sneak into the lab and replace it with balanced meals or snacks, depending on the hour, to take instead.
The young lady had been kind enough to start making healthy meals on her own so he would stop scaring her.
She had tried to ask why but Bucky had just stared silently until she promised not to enable unhealthy habits in the lab.
The girl did not need to know that it was mostly because he'd seen her drop meals and snacks off to Tony and Bruce.
And goddarnit, Bucky realized he'd started to consider the girl his too, he wondered if Steve knew. Probably because Bucky had noticed his Omega teaching Darcy their family recipes and he'd once told Bucky that he'd only teach those to their Omega children.
Bucky sighed and hid the box of poptarts and went to go see how Natasha was doing, she'd been on a mission for a couple days and had come back with a broken arm.
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A/n: Thor is definitely not used to boundaries or being told no so... And of course Jane and Darcy came to stay at the Tower because Tony's got the best lab and Darcy kind of just starts mothering, but she's more of a sister with all of her teasing and pranks.
Darcy is an Omega, it was a thing in the 30's and 40's to pass recipes on to the Omega children regardless of sex, and since neither Tony nor Bruce is very interested Steve decides to teach Darcy because Bucky has started looking out for the girl which means he's seeing her as his and that's pretty much the beginning of an adoption, which means that Steve finally gets to teach his recipes to someone because Darcy cooks, not often because she's still Jane's assistant but enough that Steve starts to teach her.
Darcy, in my headcannon for this story, is an orphan but she's relied on her instincts more than once in order to survive and so she knows that Steve and Bucky are pretty much adopting her as their kid, she's not quite brave enough to ask about calling them mom and dad aloud yet but she definitely calls them that in her head.
And eventually Loki is adopted too because you can't adopt Thor without getting his brother too, as much as I'm tempted to do a chapter for him in this story I kind of just want this fic to be the Avengers but know that Bucky and Steve probably just adopt all the lost sould they encounter because they are desperate for kids.