Restrooms, trash cans, and water fountains are essential. Tables and chairs are nice. So is protection from the sun and rain, as well as lighting for nighttime. If so, think about a bandshell. Maybe you would like to have a snack bar or outdoor cafe.
Every public space has to have rules.
Now, it's time to put it all together. You can make this a poster project or put it into the form of a report. Maybe you want to take your park from a plan to reality. It might seem impossible, but it's not. A Web site about kids around the world making things better.