Kai Barton is the oldest daughter of Clint and Laura Barton. Kai was Clint's biological daughter, but when he and Laura married, Laura adopted her and became the mother the girl had always needed. Kai was much like her father, meaning she was an amazing archer, but from a young age, she learned how to fight because of her aunt Natasha.
When Kai turned fifteen, her father had been taken under control by Loki, so Natasha promised the young girl and her family that she'd bring Clint back. Nick Fury had other plans though, since he knew how amazing Kai was with a bow and arrow, as well as in a physical fight, he recruited Kai to help defeat Loki. She worked beside her father, once Natasha had gotten him past his mind control.
Three years later, Kai was an official Avenger, much to Laura's dismay. Laura loved Kai, and she was scared Kai would end up hurt or worse because of the Avengers, much like she had worried for Clint. What the parents didn't expect was Kai to find someone she would find happiness with as much as she had her own family...
My life has been anything but normal. HYDRA killed my father than took me captive. They tortured me for years before a group called the Avengers saved me. Not even a month past by when they left me at an orphanage, thinking I would be safer there. Little did they know I wasn't safe anywhere. The girls and boys in the orphanage don't know a thing about my past and I intended to keep it that way. I'm now 14 and believe me, It was a strange eight years. I wish my parents could see me now so that I could show them the girl they gave away. They should never have left me behind.
P.S Natasha and Clint did not have Harper when Clint was with Laura. Harper was born a few years before Clint met Laura. To clarify. when Harper is 16, Cooper is 10, Lila is 7 and Nathaniel is yet to be born. So Technically Harper is half-siblings with them all. What happened with Harper is the reason Clint kept his other children and wife a secret from Shield.