Lost and Found-Adele and Simon in China by Barbara McClintock*

Adele and her brother Simon visit their uncle Sidney in China.  He takes them all over the country.  The reader experiences their adventure via postcards/letters sent to their mother plus the beautiful illustrations.
Before the trip, Uncle Sidney gives Simon many items for the trip.  At each location, Simon loses one item.  The reader is then challenged to find the item.
A very fun book (and series!)!
*Highly recommend.
-Borrowed from the library.
I love Mrs. McClintock's illustration style.