Short answers, pulled from the story.
The first purpose-built public playgrounds were created in 1846 at Peel Park in Salford and at Queen's Park and Philips Park in Manchester, following a call by Thomas Carlyle in his 1843 work Past and Present.
Emergency departments in the United States treat more than 200,000 children ages 14 and younger for playground-related injuries each year. Falls to the surface contribute to 79% of all injuries, and in 1995 the estimated cost of playground-related injuries for that age group was $1.2 billion.
Lady Allen of Hurtwood was a pioneering designer and child advocate who popularized the concept of the junk playground in post-war London, where children played with rubble and invented their own entertainment. She wrote a series of illustrated books on playgrounds and at least one book on adventure playgrounds, helping the idea spread worldwide.
The Playground Association of America was founded in 1906. Luther Gulick became its president a year later. The organization later became the National Recreation Association and eventually the National Recreation and Park Association.
Experts including Tim Gill have found that excessively safe playgrounds can decrease children's sense of achievement, increase fear, and lead older children to seek out genuinely unsafe alternative play areas. A lack of experience with heights in childhood is also associated with increased acrophobia in adults.
During the 1970s and 1980s, playgrounds could be found in almost every park across many Soviet cities. Equipment was standardized nationwide, consisting mostly of metal bars with few wooden parts and manufactured in state-owned factories; common structures included the carousel, sphere, seesaw, rocket, and bridge.