Cambridge, Macmillan, Chambers, Longman und AHD haben das auch nicht gelistet ... nur :

Hedgehog

it's rare and not common knowledge but it is correct

 1. A small or young hog or pig; a piglet.In quot. 1889: a groundhog (woodchuck), Marmota monax.

Supported, except that I disagree with the "rare" tag in connection with young hedgehogs. I don't think it's safe to infer from the absence of the term in Cambridge, Macmillan, Chambers and Longman that it's rare (I wouldn't expect to find the British English meaning in AHD). Maybe those dictionaries simply don't update their entries as often as the OED online and oxforddictionaries.com. The OED online added the entry in 2010 with citations going back to 1949. There are numerous occurrences on reputable UK sites. As stated in #2, "the word hoglet ... seems to have been in general use among those with an interest in hedgehogs since at least the mid-1990s." I can't imagine any of the hundreds of hedgehog rescue centres in the UK not using the term "hoglet". The term might not be "common knowledge" (though I might even dispute that), but then neither are the terms for e.g. male and female swans. The fact that a term is not "common knowledge" or is relatively new (60-odd years old) does not make it "rare" imho. We might as well put all the technical terminology unknown to the majority of English native speakers into the "rare" category otherwise:-).

I agree, this word for a baby hedgehog isn't rare. It is rarely found in AE sources because the animal itself is not native to North America and only present as a pet (or in a zoo, maybe), so we rarely have a need to write about hedgehogs or hoglets.

@Norbert:

we have flat, pale slugs in our garden in Jamaica. The "little" darlings are about 10-15 cm long..... but we have a resident mongoose so I'm hoping it helps keep them down.