There is also a Ragnarok Online Lost Child Quest Video Walkthrough. If you are having trouble completing the Lost Child quest, you can refer to that video.
1. Go inside the building (rachel 100, 237) just right of the building at the top left corner of Rachel. (i.e. the building with Logan standing right outside of it).
2. On the second floor of the building is a man named Vincent. Talk to him, he will tell you to find a lost child named Phoebe.
3. Go just outside the building and speak with Logan (rachel 114, 231). He will tell you to talk to Mr. Manson.
4. Mr. Manson is back inside the building. After talking to him he will tell you about Jenny.
5. Exit the building again and head left. You will find Jenny (rachel 48, 236) inside the garden. She will tell you to ask around the market.
6. First, speak with the Idle Merchant (rachel 136, 74) just below the center of Rachel. He is completely useless but you have to talk to him.
7. Now speak with the other Idle Merchant (rachel 120, 47) just below the first one. He will tell you to go to the Ice Caves.
8. Go to the Ice Caves (1 map right, 2 maps up from Rachel). Talk to the Suspicious Man (ra_fild01 244, 324) at the entrance to the caves. He will stab you and take away 50% of your HP.
9. Return to Vincent (rachel 100, 237) in Rachel. He will tell you to keep looking for Phoebe.
10. Go to the bottom right corner of Rachel by the lake. Talk to the Kid (rachel 243, 36) standing there, you will find out it is really Phoebe.
11. Now go back and talk to Vincent (rachel 100, 237), after talking to him talk to Jenny (rachel 48, 236), then Vincent again afterwards. He will give you an Old Purple Box and a Letter of Recommendation.
12. You are now done the Lost Child Quest. You will get 900,000 Base Exp when you talk to High Priest Zhed in the Rachel Sanctuary (you can get there after completing the Rachel Sanctuary Quest