Why does Laurie's mother miss the first P.T.A. meeting in "Charles"?

In the ironic short story "Charles," Laurie's mother misses the first P.T.A. meeting because the baby sister has a cold and the mother stays home with her.

The mother/narrator is very disappointed because she "wanted passionately" to meet the mother of such a boy as Charles. For, she is incredulous that such a child can exist. This is, of course, very ironic since the reader later learns that "Charles" is a fictitious name created by Laurie for himself.
However, this irony is believable because the mother is deluded about Laurie, her "sweet-voiced tot" who "forgets" to wave good-bye to her on his first day of school, and who misbehaves constantly at home. Certainly, she never reacts to his speaking "insolently" or his acts of disrespect to her. Nor does her husband respond to Charles's insolence when, for instance, the boy "climbs" into his chair at the dinner table and says to his father, "Hi, Pop, y'old dust mop."

Neither one of the obtuse parents detect the exaggerations of Laurie about the student "Charles." Nor do they realize that clearly no child would continue with such behavior without professional intervention occurring. So, when the mother attends the next P.T.A. meeting and speaks with Laurie's teacher, she is, indeed, surprised as she finally deduces that she is the parent of "Charles."