Steampunk

Wikipedia defines steampunk as involving "an era or world where steam power is still widely used—usually the 19th century and often Victorian era Britain—that incorporates prominent elements of either science fiction or fantasy." It's a very hot sub-genre now and one of its most popular authors for children and young adults is Philip Reeve. His latest, Fever Crumb, is set in a post-apocalyptic London. Critics call it "beautifully written, grippingly paced, and filled with eccentric characters and bizarre inventions." Check it out!