A Sunday-school is a prison in which children do penance for the evil consciences of their parents.

H. L. Mencken (1880-1956) American writer and journalist [Henry Lewis Mencken]

A Little Book in C Major, ch. 3, § 3 (1916)
    (Source)

Variant:

SUNDAY SCHOOL. A prison in which children do penance for the evil conscience of their parents.
A Book of Burlesques, "The Jazz Webster" (1924)