Now the Graun
has reported that the werewolf connection is totally made up - the
lobison legend was started by cowboys, while the adoption custom started with Russian immigrants in the 20th century who claimed the Tsar would do the same thing. Either way, the practice was popularized by the Peron regimes.
There's also a good comment that December 28 is Holy Innocent's Day, which is celebrated in Latin America with pranks and jokes. The poor anglophone intern who heard of this story must have fell for it.