Kidnapped! By a kid their own age?! This definitely starts the action off right in Margaret Peterson Haddix's Risked (Lexile: 770; Interest Level: Grades 3-6), the sixth book in her Missing series.
Jonah and Katherine are researching missing kids from history to find out who Jonah might really be when they come across the story of Princess Anastasia and Prince Alexei Romanov. When the doorbell rings, they can't believe it when they see Anastasia staring at them! Daniella, as she is known in Jonah's time, doesn't know who her "historical" self is, but she comes to see Jonah and Katherine after their other friend Chip contacts her. As they walk away to discuss things, Gavin grabs ahold of them all and sends them hurtling toward 1918 Russia, the very day before the entire Romanov family (including Anastasia and Alexei) are murdered.
When it turns out that Gavin was given a "dumbed down" elucidator that only travels to a specific date and time, the children know they are in serious trouble. With no way to contact help from JB, Jonah's time-traveling friend, they must get creative in figuring out a way to save not only their friends, but also their own lives as well! This has to be one of my favorite series of all time, and I am looking forward to the seventh and eighth books! (336 p.)
One of the reasons I became an elementary school librarian is so I can read children's books.