Recently I tried recalling a book from my youth. I can't accurately recall ANY of what happened, but I'm hoping the few remaining fragments might help someone out there help me. I remember the book being war themed (post apocolyptic perhaps?). The book focused on children fighting in a war against aliens/machines. I believe the children had special powers. The only accurate memory I have of the book is at the very end when the characters cross a body of water (ocean?) and fog to reach a tower where they discover the alien race has been playing with humanity, treating the war like a game. I recall everyone dying at the end, but the book ending on a hopeful note. Little more than that remains in decrepid pea brain. This is practially nothing to go on, but if it jogs anyones memory, or you can even point me towards something that sound remotely close, it'd be greatly appreciated.