The probable connotation of the words "Poor child" is that she knows Ikemefuna is not going home, but is instead going to his death.
It has been decided by the village elders that Ikemefuna will be put to death for his village's crimes. Rather than tell the boy that, however, they tell him he is going home. When Nwoye tells his mother that Ikemefuna is going home, she knows the truth of the matter. She feels sad for the boy who has lived with them for years and has become like family to them. She also knows the role Okonkwo will play in the boy's death, which will add to Ikemefuna's suffering. She pities Ikemefuna and suffers along with him.
