Hello there,
I'd also share my thoughts on Neverland. I think that Barrie explained it quite clearly what is Neverland. It can be found right in the first chapter, and it goes like this:
"I don't know whether you have ever seen a map of a person's mind. Doctors sometimes draw maps of other parts of you, and your own map can become intensely interesting, but catch them trying to draw a map of a child's mind, which is not only confused, but keeps going round all the time. There are zigzag lines on it, just like your temperature on a card, and these are probably roads in the island, for the Neverland is always more or less an island, with astonishing splashes of colour here and there (...). It would be an easy map if that were all, but there is also first day at school, religion, fathers, the round pond, needle-work, murders, hangings, verbs that take the dative, chocolate pudding day, getting into braces, say ninety-nine, three-pence for pulling out your tooth yourself, and so on, and either these are part of the island or they are another map showing through, and it is all rather confusing, especially as nothing will stand still."
So, based on this description, I think that Neverland is nothing else but the allegory of the minds of the children with all of their fantasies, their dream world, and with the real world's phenomena as well but they are modified by the children's unique and "strange" perception and world view. At least, grown ups consider them to be strange but for the children everything seem to be perfectly logical. :-)
This unique mind and world view will be lost by the time when we are already grown ups. As Barrie wrote: "On these magic shores children at play are for ever beaching their coracles [simple boat]. We too have been there; we can still hear the sound of the surf, though we shall land no more."
/This is so sad, I think.... :-(/
OH, here's an online version of the text: http://www.literatureproject.com/peter-pan/peter-pan_1.htm