When I write novels, I say that I write with emotion, which usually refers to the exclamation and reflection of a certain thing or situation. In a novel, emotional lamentation is usually a kind of emotional expression. By describing the protagonist's emotional changes and feelings about a certain thing or situation, the reader can feel the protagonist's inner emotions and inspire the reader to think. Sighing was an important way of expressing emotions in a novel. It could make the readers resonate with the novel and understand the theme and emotions of the novel more deeply.
I'm not sure as the story isn't very well - known to me specifically. But it could be the children themselves, and perhaps their parents or guardians who are also affected by whatever situation the children are in.
The main theme could be about the sorrow or grief related to children. Maybe it's about the loss of children, or the hardships children face which evoke a sense of lament.
The central character in 'the wife's lament story' is the wife. She is the one doing the lamenting, so she is at the forefront. Her husband also plays a significant role as his relationship with the wife is the core of the story. He is the one whose actions, whether it's leaving or treating her badly, have led to the wife's current state of distress. There might be other minor characters like the wife's family or the people in the place she has been exiled to, but they are not as central as the wife and her husband.
The main theme is often considered to be sorrow and loss. The wife in the story is lamenting her situation, which could include the loss of her husband's love, her separation from her home, or her general state of unhappiness.