OK, while this one is not traditional folk, it is an acapella number that is near and dear to my heart...

Uncorrected Personality Traits by Robyn Hitchcock.

Wonderfully whimsical. I won't post all of it, but here's a fragment:

So, uncorrected personality traits
That seem whimsical in a child
May prove to be ugly in
A fully grown adult

If you give in to them
Every time they cry
They will become little tyrants
But they won't remember why
Then when they are thwarted
By people in later life
They will become psychotic
And they won't make an ideal husband or wife

M