Talk to the kid hiding behind the basketball hoop to start this quest. You have to find six kids hiding in different places.
1: Inside the bank, behind the table to the left.
2: In the sewer, behind some pile of trash
3: Behind the lamp post, in front of the Tower of Peace.
4: In the dead end trail, west of the church, east of Stark's Pond
5: Behind the tree west of Mr. Slave's house.
6: In the leftmost corner of the ranch.
After finding them all, return to the playground and talk to them to complete the quest. All six of them will be added to your Friends List.