The fact that Barrie was so involved in the lives of the boys. He watched them grow, play, and dream, and he translated their experiences into the story of Peter Pan. For example, their make - believe games could be seen as the adventures in Neverland in the story.
Barrie's closeness to the Llewelyn Davies family. He was like an observer of their family life. The boys' innocent charm, their fearless exploration of the world around them, just like how Peter Pan explores Neverland, are all indications that the story of Peter Pan has real - life origins.
One fact is that J.M. Barrie based Peter Pan on his interactions with the Llewelyn Davies boys. Their playfulness and childish nature inspired him.