Before humans knew that beings existed outside of their own world, before, in fact, humans had gone much further than sending a couple of people to their local moon, they visited. They'd always managed to remain hidden, but their work was kinda starting to get noticed. They'd find those who were sick and injured, and amongst the human there were many. Mostly, they worked with kids, however. At night, when the entire area was asleep, they would take the children aboard their ship and treat their illnesses and injuries, then, before dawn, send them safely back to their homes and their beds. Problem is, someone's always gonna notice when a kid who seemed to be at death's door due to conditions like cancer, is suddenly completely healed. -- Anon Guest
To damn them with faint praise, the Vae meant well. They came to examine a pre-industrial civilisation and all the duckblinds in the world could not prevent empathy from growing in their midst. They were especially long-lived and as a result, their fecundity suffered. Therefore, they were especially fond of watching the native children.
In a pre-industrial society, there is little to prevent disease. Indeed, this culture had yet to encounter germ theory, and attributed ill health to bad smells whilst building their housing with a mixture of sticks, mud, and animal feces. The cultural medicine relied heavily on solutions that felt like they were doing any good and were only co-incidentally therepeutic.
The Vae could not stand to watch children die. They could not watch children become abandoned in the deep forests if such children were inconvenient to their parents. They could not watch infants wither. So they took matters into their own hands whilst trying to be ethical about it.