A three-year old was tasked by her father to gather foodstuffs from the sea and bring them to the kitchen for cooking. She never left the house, but was expected to find items around the house representing sea food. And the cooking was to be “pretend” cooking.
Her first scavenged item was a plush toy crab. “Good choice,” her Father responded proudly. “That will definitely go into our cooking pot.”
And then the child disappeared for a long while. Her father assumed she was looking for clam shells scavenged from the beach.
But instead, she brought back a plushy toy mermaid.
He was horrified. “Oh no, we don’t eat mermaids!”
I’m somewhat relieved that if she ever encounters a real mermaid, she will have learned that the mermaid is at least part-human, and therefore not a food item. But oddly enough, the eating of mermaids has some storied precedence. The best example I’m aware of is the Ningyo, a Japanese variant of the mermaid mythology. 
The Ningyo is a human-faced fish that some describe as being tasty, and bringing good luck if eaten. Perhaps it was inspired by carp similar to that at the right, which with selective breeding has developed some surprisingly human-like facial characteristics.
As for where the good-luck notion came from, I have no idea, and the three-year old doesn’t know either.
Most adults do not consider a variation in appendages to signify a food item. That is, if a baby has 6 legs, as was recently reported, they are nevertheless human and not food. If they have no normal appendages at all, then they are still obviously very human. Even children with the rare Mermaid syndrome (sirenomelia), where two legs are fused together into a relatively useless Mermaid-like tail, would never be mistaken as anything but wonderfully human.
So I wondered what triggered the thought in a three-year old mind that a mermaid would be edible?
Then I remembered that same three year old has caught little fish, and she remembers the fins and scales, and associated the fish catching with really tasty food. So like Pavlov’s dogs, half a fish might be enough to start the salivation response.
So sorry little mermaid, it doesn’t matter how girlish (or womanly) your top half might be, it’s your fishy half that’s gonna get fried, grilled or blackened if one kid has anything to do with it. My advice to you – stay away from preschoolers.