If you like animal books you will like Secrets at Sea. It's another great book by Richard Peck.  It reminds me a little of Poppy by Avi but with a more aristocratic air. The mice board a ship to England with their human companions.  They secretly explore the ship and find adventures at sea.  Narrowly avoiding being caught by unsuspecting humans or the ships cat. As always a happy ending that will make you smile.