You could talk about the rapid growth in a the post World War I era. Show how the automobile has brought people by the masses to the park. How company picnics came out by the dozens to ride the new wooden coasters, swimming pools, etc. Parks like Kennywood, Euclid Beach, Conneaut Lake, Riverview, Crystal Beach, Hersheypark, Cedar Point, Elitch Gardens, etc. all hosted some of their largest group outings to date, anywhere from 10,000-20,000 people at one time. Rapid growth might be formulated subject.
I have a book called "The Great American Amusement Park-A Pictorial History", by (the spelling is off) Gary Kyryzak ?, well he put out a book that has an timeless collection of photos from that era. It cost me about $125 to get a copy of that book, since some nice park enthusiast felt to need to lift it out of my hometown library. I have to fight with my owners to get it back when they borrow it.
Charles Jaques ? has some great books on Kennywood and west View Park, also in Pittsburgh, and Hersheypark. Amusement Park Books has several out, including the one on Conneaut Lake Park in PA. I am sure that the next reader can direct you to an ebay site where some of these books are for sale.
Parks of that era offered a daily getaway for the entire family at the end of a city streetcar line, and brought Coney Island style amusmements and entertainment to parks all across the country.