Print out a blank passport for each child. You may find a blank passport for printing at Enchanted Learning.
Print out the passport, and have the children cut them out along the designated lines. Fold the pages in half to create a booklet, and staple along the fold.
Allow each child to personalize her passport with colored pencils or crayons.
Purchase a date stamp from an office supply store. With a date stamp, mimic a "real" passport and add a new date stamp to each activity in the passport.
Encourage children to pick up mementos along the way on their trip, such as postcards or stickers to place into the passport. Take a picture of the child in front of a monument or attraction, so they may cut and shape the picture to place into the passport.