In looking for instances of poglet, I came across this note from Sidney Baker, The Australian Language: An Examination of the English language and English Speech as used in Australia, from Convict Days to the Present, with Special Reference to the Growth of Indigenous Idiom and Its Use by Australian Writers (1966) [combined snippets]:
Many of the expressions listed above have long since ceased to be remembered. One of the terms, only briefly mentioned, which has had a quite extraordinary history is wog. Long before Australian soldiers took it to North Africa and called an Arab a wog, it was used in a different context in this country.
We first began to employ it extensively in the early 1930s (perhaps the 1920s, but certainly not as far back as World War I) to denote a germ or parasite, a speck of dirt, any small insect or grub. Possibly a wog was even smaller than this originally ...
The term, also used in nursery parlance for a child, was probably shaped in these applications by the English dialectal polliwog or polliwig, a tadpole. In his "Dictionary of Americanisms" (1889) Farmer lists the U.S. use of polliwog similarly. Australian nursery elaborations of wog include woggy, poggy (by rhyme), pog-wog, poggy-woggy, poggy-wog, poglet, poggles, poggle-pie and poggle-top, all used as endearments. These introduce an interesting reversion, for pug as applied to a child or person was used as an endearment and diminutive in sixteenth-century English. (The word survives in pug-dog.)
The elaborations pog-wog, poggy, etc. apparently emerged independently, in spite of the fact that Boldrewood, "Ups and Downs" (1878), p. 94, refers to "the pug-wuggies, or little people", which would indicate a lengthy Australian association with the expression.
I also note that Christopher Milne, Beyond the World of Pooh: Selections from the Memoirs of Christopher Milne (1998) named a replacement for one of his stuffed animals "Poglet":
The author remains the author always. The character may well grow out of his part. At the age of seven I was quite pleased when a large Piglet arrived in a box with his creator's best wishes. He was much more handsome, indeed frankly much more appealing and lovable, than my one (who was by this time in a rather dog-bitten state). I christened him Poglet, and he and Pooh accompanied me on one of my visits to Littlehampton. But had he arrived five years later, his welcome would have been cooler. Anyone wanting to make toy Piglets to send to the little boy in the book had to study the back of the title page to be sure that the little boy was still a little boy.
From these two references, one might reasonably conclude that poglet and pogger are probably extemporaneous endearments, influenced, perhaps, by piglet and pollywog, but not (until recently, anyway) slang terms for a hedgehog.