The Libraries have a LOT of e-journal subscriptions and hundreds of databases designed to help you find them. You can use PRIMO, the main catalog, to find interesting secondary sources (like articles!). For specialized US history topics, you may want to try America: History and Life. Both work in a similar manner.
Lets' say my topic is history of American children's toys, so I try
children AND toys AND "United States"
If you're interested in something like the history of Children keeping pets, start with something basic like children AND pets