When I read the blurb for Neptune's Children, my first thought was: Gone by Michael Grant. The basic idea of both novels is the same, all the adults disappear, the children are left to fend for themselves, cliques form etc. I thought that I would like it considering it was like Gone. But I didn't like it. I didn't like it very much because it was very predictable. You always knew who was going to cause problems. Another reason I didn't like it was because I had already read Gone. I had a picture in my head that was similar to what happens in Gone. I believe I would have liked Neptune's Children if I hadn't read Gone before. I would give it 2 stars just because it was very predictable.
Here is the Goodreads link for Neptune's Children: http://www.goodreads.com/book/show/2590733-neptune-s-children