This page of the Baldur's Gate 3 guide has a walkthrough for Child's trial quest. This walkthrough will help you complete the quest.
- Save Arabella;
- find Arabella's parents.
This mission is activated while staying in the Druids Grove. When you head towards the holy pond, you will come across a group of people (M3;16). It turns out that Khaga trapped a girl named Arabella in the Emerald Grove (M3;18).
Go to the designated place and save the game immediately. If you decide to talk to Khaga, you'll find out why she's holding Arabella. At this point, you will be able to influence the course of events:
- pass the nature or persuasion skillchecks - this will save the girl. The required values are very high, so you will probably need to load the game several times to achieve the desired effect;
- don't interfere - the girl dies;
- attack Khaga - you will have to fight Khaga. Arabella will die anyway.
Regardless of how the situation ended in Emerald Grove, go back to the area where the people gathered earlier. That's where you will find the girl's parents. If Arabella survived, you will get a bonus reward.