In the field of history, library catalogs can be used to locate both primary and secondary materials (mostly books).
In HathiTrust you can find children's books by using the follwoing phrase in the Subject of a Catalog or Advanced Full Text Search:
Look for reports from different cities by including a city name in the title
Library Catalogs (such as the UVM Library Catalog or WorldCat) use predefined terms to describe primary sources. Among the most commonly used terms are: