This appears to be a non-standard or invented word; it could theoretically mean a small creature with flippers, but it's not in standard dictionaries.
If real, it would be a blend of 'flipper' (a swimming limb) plus the diminutive suffix '-ling.' However, this word doesn't appear in recognized English lexicons.
The '-ling' suffix creates endearing diminutives (duckling, gosling, yearling), so 'flipperling' *should* be a word for a baby seal or penguin—it's so logical that it's surprising it isn't official.
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