Irony of gender
While Helen is forced to hide away in France to have her baby, she tells everyone that her child is her brother's. This is because her brother would face less judgment than she would, as she is a woman. As such, we see an ironic difference in the treatment of the siblings, due to their respective genders.
Irony of parentage
Helen is Michael's mother, but he believes that she is his aunt. This is because she had to lie, as having a baby out of wedlock was "improper." Michael asks Helen if he can call her "mummy," and ironically she is actually his mother.
Irony of death
As a child, Michael tells Helen that he will hurt her with his death. Helen then replies that she will be dead by the time that happens, as she is a lot older. However, Michael then enlists to the war and is killed.
Irony of Michael's mouth
Helen tells everybody that she cannot abandon Michael because he has her father's mouth. To the residents, they think that this is because Michael is George's son, however Michael has his grandfather's mouth because he is actually Helen's son.
Irony of warfare
During his time in warfare, Michael writes Helen a letter saying that "there was nothing special doing and therefore no need to worry", however just after this "a shell-splinter dropping out of a wet dawn killed him at once."