My tween nephew has really been into the Horrible Histories books for a few years, and has really enjoyed them. For those of you not familiar with them, this is a series of illustrated books for kids that describe a lot of history, with an emphasis on things that are gross or outrageous and hopefully, thereby, exciting or appealing to adolescents. This has been spawning an interest in learning more about history, and it seems like he's ready to move up to slightly more sophisticated stuff (although I don't suspect he'll tolerate anything really dry and academic). Members of /r/AskHistorians, what books can you recommend for a young person who wants to read fun, but historically sound, books about history? I'm particularly interested to hear if there were books that you read when you were young, and which maybe helped excite you about history at an impressionable age, but I'm also happy to hear about anything else you might recommend.
A fantastic book is Never Caught, the Story of Ona Judge: George and Martha Washington's Courageous Slave Who Dared to Run Away by Erica Armstrong Dunbar and Kathleen Van Cleve, a young reader's edition of Dunbar's biography of Ona Judge. Judge was an enslaved person who escaped from slavery while George Washington was president. For a younger reader, it would bring attention to the stories of marginalized peoples, in particularly enslaved persons, and the system of slavery in the early republic, especially since it's tied to the Washingtons.
A series emerging in the 1970s by David Macaulay including Cathedral, (Roman) City, and Castle were well done, entertaining and extraordinarily illustrated. I believe they still hold water, and they may be a next step for your nephew.