You must complete this quest within time limits if you want to keep Cernd in party.
Cernd's Child is a companion quest which starts when you return to Athkatla from Trademeet with Cernd in your party, you will meet Igarol, Cernd's former neighbour, who will tell Cernd that his wife had a child nine months after Cernd and his wife let Cernd go to follow his call for nature.
Speak to Fennecia in her home marked on your map, which is also in the promenade. She will tell Cernd to get out of her house. After Cernd leaves, talk to Fennecia again. She will tell you that Cernd's wife stayed with a noble named Deril and that she died under suspicious circumstances. She will also tell you that Cernd's child is in Deril's home.
Enter the Deril Estate in the Athkatla Government. After Cernd threatens the servent Glut, Deril will appear. If you advise Cernd to threaten Deril into giving him the child, Deril will give Cernd the child and disappear. Cernd will leave your party to bring the child to the Druid Grove and he will ask to meet him there. He will offer his services to the party once again and you will receive experience as a reward.