What is your favorite type of map? I found a National Geographic map of California from the 1950's in my dad's attic this summer. AAA maps and trip-tiks. Hand-drawn city maps with local attractions. Maps of intricately detailed islands. Maps are a simple project requiring just basic paper and pencil or pen.
See what intrigues your kids. A "real" map of their backyard, room, school, classroom, a park? The idea here is NOT accuracy, it is getting kids to think it new ways. If they like what it looks like, that's cool. It may help to think about whether they are looking at the park from a helicopter or Imaginary worlds are even more fun ~ an imaginary amusement park or treasure island with buildings and natural wonders. Encourage creative naming for everything from streets to stores to mountains.
The first two maps of imaginary cities were drawn by my daughters this summer and currently up on the wall. Next a map of a park drawn by my younger daughter and a map of the school grounds and a map of a candy world drawn by my older daughter.