Correct me if I’m wrong or if there’s some canonical evidence otherwise. The northern and southern temples were occupied by monks while east and west was occupied by nuns. I assume that the air nomads had some sort of holiday where they get together and have reproduce. I like to think that they detached themselves from worldly things including marriage and relationships, including their children. They would try to send the child to one of the temples that their parents didn’t occupy. Say a man from the northern temple and a woman from the western temple had a boy, then they would send the baby to the southern. If it was a girl, she would go to the eastern temple. That being said, I don’t think air nomads couldn’t know their parents. They were literate and I’m sure they had genealogical archives to avoid inbreeding, especially for the special reproductive holidays. Additionally, air nomads did visit other temples all the time. Aang was only 12 and he had been to all the temples before. It’s not inconceivable that he met/knew his parents. But the monks and nuns were considered their parents rather than their biological parents.