Harry Potter was three when they sold him.
His step-mother's family hates magic, so they hate him.
When they heard about people who pay top dollar for "freaks" they couldn't resist the opportunity.
So, off Harry Potter went.
To Hydra.
They were brutal.
They beat, shoved, and tourtured the boy. They made him use his magic to power their sheilds and taught him how to fight. Within a year, Harry could kill a man a dozen ways without a weapon. Hlaf on those methods, he didn't even need his hands for.
Harry didn't want to kill. He wanted to be good. He knew his Daddy From The Skies would save him.
Luckily, Harry never left base. They needed his magic to protect them.
Wanda and Pietro loved Harry. The sweet little boy with his five ratty stuffed animals, and his too big clothes, and his stories.
They knew they were just using Strucker for the power. And when they got out, they'd take the boy with the dark hair, green eyes, broken glasses, and big heart with. They'd help him find his Daddy From The Skies.
They didn't care that Harry couldn't speak.
They didn't care that he could barely hear.
On Harry's seventh birthday, they came.
The Avengers.
Hydra told Harry to pack up his things and be ready. So, his wolf, dog, deer, snake, and panther went in his backpack with his spare glasses, hearing aids, and his picture his dad with his uncles Moony, Padfoot, and Snivillous.
He pushes his magic into the shield and let his spirit free as he did so.
Harry's very essance entered the barrier.
So, when Iron Man hit the sheild and yelled, "Shit" only to have Captain America yell, "Language!" he couldn't help his silent giggles.
And, being the micheivious kid he is, he opened the sheild just enough for the metal man to slip through.
When he went through, unharmed, laughing and shouting, "Suck it Cap! I said shit and it let me through! How's that for language?" Little Harry doubled over with silent laughter.
He continued to watch and listen and the heroes told jokes and had conversations while they fought. Black Widow was like Moony. Sarcastic and Serious. She was quick to repremend the others. Loki was like that too. But Iron Man was just like Padfoot. Everything was funny and a joke.
Harry already loved them.