Danger At the Zoo by Kathleen Ernst

In this book, "Danger at the Zoo" the main character girl named Kit and boy named Will open the zoo gates and unveil a whole lot of danger, when actually the gates are supposed to be kept closed. The reason behind the danger at the zoo is because once the gate is opened by Kit and Will, you can imagine the different kinds of dangerous animals that were let out...and then their adventure and mystery of getting the animals back in the zoo begins.  It's a great book to read because there is mystery and it also sends a message about being responsible and kind towards animals.