A. N. Wilson begins a book review in The Spectator with this splendid anecdote:

Ronald Knox, found awake aged four by a nanny, was asked what he was thinking about, and he replied “the past”.

A remark with a similar weight of world-weariness was made by my eldest son, when he was but a tot. Having contracted some sort of stomach bug, he vomited. As we mopped his fevered brow, he wailed “Oh, why can’t I have a happy life?”