Harris's body was left in an abandoned lot.
Seven-year-old and 8-year-old boys were charged, but prosecutors later realized they had made a mistake. A 29-year-old man was later convicted of the crime.
Sunday's picnic was held at Ryan Harris Memorial Park at 67th Street and Lowe and included a balloon release.
Two months ago, a relative of Ryan Harris was killed at that park in a random shooting. On Sunday, family and friends remembered both Harris and 30-year-old Shaneda Lawrence.