All playgrounds should have adult supervision while being accessed by children, mainly because kids will always use equipment in unintended ways, that expose them to greater chance of injury, often of a much more serious nature. This doesn't mean someone of adult age sitting on a nearby park bench glued to their cellphone screen, completely oblivious to anything taking place on or around the playground. Adult supervision needs to be constant and free of any distraction, sometimes requiring more than one adult for situations where there are many children or overlapping age ranges and respective nearby play areas. 

A toddler or preschooler may need to be redirected to their age appropriate play area instead of being allowed to enter and play on an area designed for 6 to 12 year olds, where it's unsafe for a younger child who's likely to land on their face or head in a fall impact. Likewise, older kids can quite literally destroy a play area designated for children 5 and under, by using everything in unintended manners or going beyond established weight limitations and causing damage. 

It's also important to step in during any conflict that might rise to a more serious and potentially dangerous level, before something happens by those children involved not paying attention to their surroundings and equipment, usually ending up impacting it and resulting in an injury. If an emergency arises, the adult needs to take appropriate action, including summoning an emergency response, and caring fo the injured child until help arrives. 

An adult also has the ability to recognize higher and lower levels of loose-fill safety surfacing, where high areas can fill in lowered areas with a simple sideways brush or two from their foot. If any form of dangerous hazard is observed, an adult can report this for further inspection and repair or replacement, which benefits every child who visits that playground.