Hobbits and Borrowers (both modern inventions): yes, both male & female are described.

Iodine deficiency: I may be wrong, especially about the hillbilly connection, but if I recall correctly the interview with a public health advocate, average IQs of American schoolchildren jumped quite a few points in many inland areas when iodized salt became mandatory. Goiters (symptom of extreme iodine deficiency) are rare but subtler, generally unrecognised effects of low-level deficiency even today retard neural development in populations in many regions of the world. But I'm no expert. Certainly the "hillbilly" stereotype depended on lack of education and communication, whether or not other factors contributed.

Leprechauns as ethnic caricature: the CBC radio documentary which mentioned the caricatures and similarity to FAS symptoms, implied this Irish folklore figure was previously familiar enough to borrow for English cartoons. These in turn shaped the popular image of leprechauns to this day. Some of the features representing the Irish to the English public and caricaturists of that day may actually have been symptoms of poverty. Is this implausible?

Swift satirised another side of the same stereotypes and economic policies in his "A Modest Proposal": to this unforgettable "remedy" there could be not one objection as it was designed only for the "kingdom of Ireland, and for no other that ever was, is, or, I think, ever can be upon Earth."

Jeri, did the slidey tracks get bigger as they descended? Any overhanging branches near the top end? Possible rolly tracks instead? (Wee folk bowling? Ravens, like otters, have been seen repeatedly sliding down a snowy slope "cawing vociferously" but from your description these tracks were tiny.)