Where do you live that you're seeing "used needles littering many of them"? This was something that I often heard talked about by teachers and parents, but I only ever recall seeing ONE used needle laying around when I was a kid and it wasn't at a park - it was on the campus of an Ivy League college!

The vast majority of the parks I've been to in the US have been clean and well kept up, even ones in the higher-crime areas of town.