Two books that we have been reaching for time and again this summer are Our Great Big Backyard and Larry Loves Seattle.
For obvious reasons, we have been loving the Seattle related book as it has given us a great way to discuss our move with James Robert and get him excited. We have read other books in the series that are just as fun (especially the Chicago one) and would definitely recommend them for the toddler age reader.
The other book in heavy rotation is perfect for summer, Our Great Big Backyard, is all about our National Parks and the adventures a family takes over summer vacation. At this age, James Robert loves to look at the map and trace their trip. He also gets a kick out of the characters pretending to be cowboys and pirates. It's a fun book with lots to teach.