In the fantasy poem "The Forsaken Merman" by Matthew Arnold, the speaker or narrator is the merman of the title. According to the Merriam-Webster Dictionary, a merman is "a fabled marine creature with the head and upper body of a man and the tail of a fish." In most legends, mermen can assume normal human shape and come up on land, at least for a limited time. Arnold's poem assumes that humans can also convert to mermaids, because the premise of "The Forsaken Merman" is that a human woman named Margaret fell in love with him and left the land to live with him under the sea. However, she hears the bells of Easter ringing in the town church, goes up on land so that she can pray, and then never returns. The merman is sorrowful over his lost love. He considers her cruel because she left.
The children he is calling are the children that he and Margaret had together. Evidently, Margaret stayed in the sea for a long time, because she and the merman have a family. When she forsook the sea and went to the church, her children stayed behind with their father. Perhaps, because they are offspring of a merman and a human, they are unable to live long on land, or perhaps, because they have spent their entire lives under the sea, they are unwilling to leave it. They long for their mother to return to them. Their voices are "wild with pain."
The merman and the children even take human form and go up on land to call to Margaret, but she ignores them. They are forced to go back alone, without her, and lament their loss in their home beneath the waves.