What do the lost boys symbolize in Peter Pan?

According to Peter Pan, the lost boys are "boys who fall out of their prams when the nurse is looking the other way and, if they are not claimed in seven days, they are sent far away to the Neverland."
The lost boys can be understood as a symbol for all orphaned children. This is why Barrie presented them as carefree, playful, and—more often than not—naughty and ill-behaved, as they've basically grown up without adult supervision or guidance. By the end of the novel, they realize that they cannot stay with Peter forever and decide to return to London with Wendy.
Barrie believed that all children should grow up happy and loved and should be able to love in return. The fact that all of the lost boys end up being adopted and grow up into good and kind adults who live comfortable and fulfilled lives only solidifies the point that Barrie was trying to make.