Magic Treehouse: 1-28: Eight year olds trespass, get sent to the past, and nearly die (repeat 28 times)
Magic Treehouse 29-: Crazy librarian sends children on dangerous missions to the past to steal stuff
I haven't read Alcatraz, (I know, I totally need to) but I can tell you that Reckoners and Rithmatist are both wonderful. (Warning you'll be begging for the sequel on Rithmatist)