The Missing Series by Margaret Peterson Haddix

After helping Chip and Alex survive 15th century London, Jonah and Katherine are summoned to help another missing child, Andrea, face her fate. Andrea is really Virginia Dare, from the Lost Colony of Roanoke. Jonah and Katherine are confident in their ability to help Andrea fix history, but when their journey goes dangerously awry, they realize that they may be in over their head. They've landed in the wrong time period. Andrea doesn't seem that interested in leaving the past... moreAfter helping Chip and Alex survive 15th century London, Jonah and Katherine are summoned to help another missing child, Andrea, face her fate. Andrea is really Virginia Dare, from the Lost Colony of Roanoke. Jonah and Katherine are confident in their ability to help Andrea fix history, but when their journey goes dangerously awry, they realize that they may be in over their head. They've landed in the wrong time period. Andrea doesn't seem that interested in leaving the past. And even worse, it appears that someone has deliberately sabotaged their mission... less

Still reeling from their experiences in Roanoke in 1600, Jonah and Katherine arrive in 1611 only moments before a mutiny on Henry Hudson’s ship in the icy waters of James Bay. But things are messed up: they’ve lost the real John Hudson, and they find what seems to be the fabled Northwest Passage—even though they are pretty sure that that route doesn’t actually exist... moreStill reeling from their experiences in Roanoke in 1600, Jonah and Katherine arrive in 1611 only moments before a mutiny on Henry Hudson’s ship in the icy waters of James Bay. But things are messed up: they’ve lost the real John Hudson, and they find what seems to be the fabled Northwest Passage—even though they are pretty sure that that route doesn’t actually exist. Will this new version of history replace the real past? Is this the end of time as we know it? With more at stake than ever before, Jonah and Katherine struggle to unravel the mysteries of 1611 and the Hudson Passage...before everything they know is lost. less

Jonah and Katherine come face to face with Albert Einstein in the fifth book of the New York Times bestselling The Missing series. Jonah and Katherine are accustomed to traveling through time, but when learn they next have to return Albert Einstein’s daughter to history, they think it’s a joke—they’ve only heard of his sons. But it turns out that Albert Einstein really did have a daughter, Lieserl, whose 1902 birth and subsequent disappearance was shrouded in mystery... moreJonah and Katherine come face to face with Albert Einstein in the fifth book of the New York Times bestselling The Missing series. Jonah and Katherine are accustomed to traveling through time, but when learn they next have to return Albert Einstein’s daughter to history, they think it’s a joke—they’ve only heard of his sons. But it turns out that Albert Einstein really did have a daughter, Lieserl, whose 1902 birth and subsequent disappearance was shrouded in mystery. Lieserl was presumed to have died of scarlet fever as an infant. But when Jonah and Katherine return to the early 1900s to fix history, one of Lieserl’s parents seems to understand entirely too much about time travel and what Jonah and Katherine are doing. It’s not Lieserl’s father, either—it’s her mother, Mileva. And Mileva has no intention of letting her daughter disappear. less

Jonah thought that after his last adventure in 1903, he and his sister Katherine would have a break from time travel for a while. For the first time, he’s willing to look into his own identity in the past, and he thinks this is his chance. But he barely has time for a single Google search before he, Katherine, and their friend Chip are tricked and zapped back to 1918--and to the house where the Romanov family was imprisoned after the Russian Revolution... moreJonah thought that after his last adventure in 1903, he and his sister Katherine would have a break from time travel for a while. For the first time, he’s willing to look into his own identity in the past, and he thinks this is his chance. But he barely has time for a single Google search before he, Katherine, and their friend Chip are tricked and zapped back to 1918--and to the house where the Romanov family was imprisoned after the Russian Revolution. Trapped without a fully working Elucidator, the three kids still hope they can escape and save the lives of Anastasia and Alexei Romanov. But is it possible to change time that much when modern-day scientists have identified the entire Romanov family’s remains? Description from http://haddixbooks.com/books/risked.html . less