Mustard soup works (Situational Irony)
Arty must eat the mustard soup his grandmother made for him, but the taste of it is horrible and he doesn't want to. A big deal is made of how bad the soup is, especially when, in a letter, Eddie remembers having to drink the soup when he was little. Ironically, though the soup has become infamous for tasting terrible, it actually makes Arty feel better and cures him of his fever.
Behind the Malted Machine (Situational Irony)
At the end, Grandma asks if Arty and Jay were looking for her money. They pretend that they were not, thinking that she would become livid if she found out they were trying to steal from her. In a comic moment, she tells them, "You should have looked behind the malted machine." This is an uncharacteristically cheeky moment, and it is ironic that Grandma is playing along in the logic of their thievery, even though they have been so afraid of her.
"Glad you're safe with my family" (Dramatic Irony)
In one of his letters, Eddie tells the boys that he's "glad [they're] safe with [his] family." The irony lies in the fact that they are not safe at all. They are living with an old woman who has been abusive in the past, a forgetful, mentally-disabled aunt who cannot remember where her own apartment is, and a mobster uncle who's at risk of getting whacked. There is a humorous disconnect between Eddie's characterization of the boys' situation and what is actually going on. While the audience is privy to the risks that the boys face, Eddie is benignly unaware.
Bella is in love (Dramatic Irony)
Bella makes a confession to Arty and Jay, what she calls their "sacred secret," that she is in love with Johnny the usher and intends to marry him. The audience then spends a long time aware of this fact, while Louie, Gert, and Grandma have no idea. We know that protective Grandma will not approve, but Bella doesn't want to tell her until the time is right, thus creating an instance of dramatic irony.
