why does jem say boo must not be home. what is ironic about? why might it be important for him and scout that boo should not be home?

The children are out walking alone at night, and it gives them a sense of comfort that Boo is not there, and they have one less thing to worry about. Ironically, there's a mockingbird singing in Boo's tree, and Jem says that Boo can't be at home because it's there...... never giving a thought to the fact that Boo is a mockingbird...... and not knowing that he'll save them from Ewell's attack.