Fury had strict rules about children on the Hellicarrier, all of which Clint and Natasha broke when they had, what he like to call, the "terror twins." So, he put in more rules and regulations, chief among them being that the twins weren't allowed out of their family's apartment without authorized adult supervision. Unfortunately for him, five-year-old Artemis and Apollo Barton thought that it was a rule made to be broken.
Apollo was laying on the couch in the living room of his family's apartment. His sister Artemis was doing a handstand on the other side of the couch, with her back pressed against the backside of the couch. She was trying to see how long she could hold the position, and so far she'd been at it for five minutes.
"Artie," Apollo sighed, "I'm bored."
"Then go do something."
"But Artie!" Apollo sat up, resting his chin on the top of the sofa, looking at his twin.
"But Pollo'! I'm trying to break my record."
"Artemis, please. Let's do something!"
She groaned, pushing her feet against the back of the couch and bending backward to flip herself upright. She rested her arms on the back of the couch, next to her brother, "Fine. What do you wanna do?"
"We can spy on Fury." Apollo suggested, "Or go do target practice? Oh! Or we could go 'sploring in the archives!"
Artemis hummed, "I do like exploring the archives. That sounds fun. Let's go!" She leapt over the back of the couch, grabbing her brother's hand and dragging him down the hall to her room. The two of them locked her door before scrambling on to the bed. Apollo crouched down on all fours, and his sister climbed on top of him, standing on her tip-toes. She reached for the air vent and carefully pulled the cover off, dropping it to her bed. Artemis pulled herself up into the air duct, before reaching down and helping Apollo up behind her.
The two crawled through the air ducts until they came to the archives. Together, they pushed the cover off before jumping down to the ground.
"So, what do you wanna look at first?" Apollo asked.
Artemis looked around like a kid in a candy store, "I wanna read about Agent Carter!"
Apollo grinned, "Okay, the C's are this way!" He grabbed his sister's hand, leading her down the aisles of files until they found the ones she wanted. They sat there, reading and playing pretend for hours.
And if Coulson happened to find them later, knee deep in files about Agent Carter and Captain America, he wasn't saying. And he certainly didn't sit down on the floor with them and tell them all the stories he knew that weren't in the files.