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Forget Elf on the Shelf: Worry about Hello Barbie, actual child surveillance toy
https://www.toytalk.com/hellobarbie/privacy/
Search for 'research' or 'data analysis'.
At a bare minimum, Mattel now has a 'focus group' of every child they have successfully sold to. And they will use the data gathered to help them sell more Barbies. Possibly by making better Barbies. (But more likely by learning how to manipulate children into wanting more Barbies.)
Maybe Elf on the Shelf 'prepares children for the surveillance state.' but Hello Barbie makes them actually live in one?