Caught by Margaret Peterson Haddix (Lexile: 730; Reading Level: Grades 5-8) is the 5th book in the Missing series about children who were kidnapped out of their proper places in history. Jonah (one of the kidnapped children) and his sister Katherine have been trying to return the children to their proper timelines to repair history.
In Caught, Jonah and Katherine travel to the early 1900s in Switzerland and Serbia to return Lieserl (Albert Einstein's daughter) to her proper timeline. Travel through time is getting more and more complicated because of the interference of Second and others who don't want to return history to it's proper path. And, the children know something is really off when they realize that Albert Einstein is studying time travel (which wasn't part of the original history) and his wife seems to know they are there (despite them being invisible). And, there is another little complication when Jonah and Katherine realize what really happened to Lieserl in her time. Will they be able to allow that event to really happen?
This is one of my favorite series, especially because it is a fun mix of science fiction (time travel) and historical fiction (about the time period to which they travel). This is a series you should probably read in order, so if you haven't tried it yet, start with Found. I am also looking forward to book 6: Risked, which was just published in September. Caught has 343 pages.
One of the reasons I became an elementary school librarian is so I can read children's books.