In its natural state, the child tells the literal truth because it is too naive to think of anything else. Blurting out the complete truth is considered adorable in the young, right smack up to the moment that the child says, “Mommy, is this the fat lady you can’t stand?” At this point, the parent rightly senses the need to explain kindness.

Judith Martin (b. 1938) American author, journalist, etiquette expert [a.k.a. Miss Manners]

Miss Manners’ Guide to Rearing Perfect Children, ch. 8 “Extra Credit,” “Ethics” (1984)
    (Source)