Yeah, back when tireswings were tires.. playgrounds used to be Darwin's swimming pool. And yeah, I jumped into a swimming pool thinking there was water in it too so that's not hyperbole either. Kids these days lemme tell ya.
So, it's probably that weird industrial foam that's in so many parks and playgrounds now. First time I saw it in a park I was like "why the fuck is there hard asphalt right under the swings?" but it's actually this strange foam that looks like asphalt but has the cushioning effect of like a gym mat or something.