“Like a lamb to the slaughter” refers to Auggie having been home-schooled by his parents in an effort to protect him from the taunts and bullying that comes with having a terrible facial deformity. But Auggie's Mum decides it's time for him to taste the real world. But his Dad refers to the sentence « Like a lamb to the slaughter ». Meaning they’ll be putting August in danger, or in a dangerous and different environment.
In other words: “Like a lamb to the slaughter” refers to Auggie having been home-schooled by his parents in an effort to protect him from the taunts and bullying that comes with having a terrible facial deformity.
