The topic may seem an odd choice for Mr. Chudacoff, 64, given that he has no children of his own, but then again, Mr. Chudacoff is also the author of a book about bachelors (“The Age of the Bachelor,” Princeton University Press, 1999) even though he has been married for nearly 40 years.  He became interested in the idea for this latest book after coming across a book from the 1950s by Robert Paul Smith titled “Where Did You Go? Out. What Did You Do? Nothing.”  “He was trying to show that adults can be too intrusive,” Mr. Chudacoff explained. Children want to keep their world private, and “it was that world outside of adulthood that I tried to get access to.”  It was a hot, muggy day in Providence, and Mr. Chudacoff was standing in the middle of a small, brightly colored playground with a rubberized base beneath the swings and soft wooden chips around the plastic slide and monkey bars. With school out, many children were at camp or on vacation or in an air-conditioned living room watching television. Wherever they were, though, they were not here. The playground was deserted.  Playgrounds first found their way to the United States from Germany in the 1880s. They spread after the turn of the 20th century, Mr. Chudacoff said, with the idea of keeping children, particularly immigrant and working-class boys, from running wild on the streets of growing cities and from the seductive lure of pool halls and penny arcades.  Boys and girls were segregated, and trained supervisors kept watch. The idea was not simply to provide a play space but also to instill virtue.  Playground supervision “makes it a school of character and of all the social virtues,” Henry S. Curtis, a psychologist who helped form the Playground Association of America in 1906, declared, “whilst the unsupervised playground is apt to get into the hands of older boys, who should be working, and train the children in all of the things they ought not to be trained in.”  Today playgrounds are once again a topic of public debate, only now concerns for educational and environmental values have replaced moral ones. An environmentally friendly restroom with a planted roof and walls is planned for a playground that a celebrity architect, Frank Gehry, has agreed to build in Battery Park in Lower Manhattan.  Meanwhile, the Rockwell Group has designed a play area for South Street Seaport in Lower Manhattan that is based on the “adventure playgrounds” popular in Europe, where there are lots of loose parts, like blocks and buckets, so that children can express their creativity.  What strikes Mr. Chudacoff about the new designs, though, is their built-in need for attendants or “facilitators” — evidence of the familiar impulse to impose adult control.  As Ms. Clark notes, “Parents are thinking that they’re helping kids with play that has a goal.” But she adds, “It’s not really play, because play is something that’s self-determined.”  Mr. Chudacoff grew up in Omaha, the eldest of three children. In the late 1950s and early ’60s, he worked in his uncle’s toy distributing business during summer holidays. “I worked in the warehouse, loading and unloading toys, and packing boxes to be shipped,” he said.  It was right around the time that the toy business was transforming itself. In 1955 “The Mickey Mouse Club” had its premiere on television, running five days a week and sponsored partly by the Mattel Toy Company. Mr. Chudacoff quotes Sydney Ladensohn Stern and Ted Schoenhaus in their book, “Toyland: The High-Stakes Game of the Toy Industry”:  “Mattel’s decision to advertise toys to children on national television 52 weeks a year so revolutionized the industry that it is not an exaggeration to divide the history of the American toy business into two eras, before and after television.”  It divides the history of play, too, Mr. Chudacoff said, because while commercial toys have almost completely colonized children’s free time, for most of history, play primarily meant roaming around the countryside or improvising with objects found or made at home.  Mr. Chudacoff led the way to a small, old-fashioned Providence toy store, Creatoyvity, which carries hardly any toys licensed from television and movies. Mr. Chudacoff looked over the figures of knights and kings, gorillas, giraffes, cows, monkeys, rhinos, chickens and dinosaurs, as well as the beads, blocks, paint, glitter, trucks, cranes, tractors and wooden toys imported from Germany.  “It’s a toy store rather than an entertainment center,” Mr. Chudacoff said, explaining that with so much commercial licensing, toys have become more of an offshoot of the television and film industries than elements of play.  One result is that a toy comes with a prepackaged back story and ready-made fantasy life, he said, meaning that “some of the freedom is lost, and unstructured play is limited.”  Video games put more of a straitjacket on imagination, he complains. And online versions of traditional games like Monopoly don’t permit players to make up their own rules (like winning money when you land on Free Parking), to harvest the fake money and dice for an altogether different game or even to cheat.  Janet Golden, a historian at Rutgers University in Camden, N.J., who is writing a history of babies in the 20th century, points out that when Dr. Seuss’s “Cat in the Hat” was published, in 1957, there were “objections to children using their imaginations — it was subversive” for them to be on their own without the watchful eyes of a mother.  Looking back at diaries, baby books and letters before World War II, Ms. Golden described how people would matter-of-factly write about how “the baby fell down the staircase, the baby fell out of the window.” It used to be accepted, she said, “that in the world, there was a lot of danger, and things happened.”  Sitting on the edge of a slide in the Providence playground, Mr. Chudacoff said that he has two great-nieces who go to a nearby elementary school that doesn’t permit children in kindergarten through third grade to run, jump rope or throw balls during recess for fear of accidents.  “What do they want them to do?,” he said, shaking his head, “stand around and buy drugs?”  A version of this article appears in print on , on Page E1 of the New York edition with the headline: Child’s Play Has Become Anything but Simple. Order Reprints| Today's Paper|Subscribe
The tension between how children spend their free time and how adults want them to spend it runs through  “Children at Play: An American History”  like a yellow line smack down the middle of a highway.