Children _must_ steal the sugar sometimes.

They _must_ occasionally spoil just the things one doesn't want them to spoil.

And they _must_ occasionally tell stories--tell a lie.

Circumstances and life are such that we must all sometimes tell a lie: just as we wear trousers, because we don't choose that everybody shall see our nakedness.

Morality is a delicate act of adjustment on the soul's part, not a rule or a prescription.
Beyond a certain point the child _shall_ not pull the cat's tail, _or_ steal the sugar, _or_ spoil the furniture, _or_ tell lies.