Thomas Allibone Janvier - The Aztec Treasure-House (1890)
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This novel seems to be a reasonably acceptable adventure story according to the reviews I found (I've only skimmed bits of it) but is posted because it exists in both a standard edition and one "for boys". (Presumably girls weren't expected to care about Aztecs or treasure.)
The story is narrated by a professor who wants to find remnants of the Aztecs and who speaks with the name-dropping and historical references that Janvier thought appropriate for such a person. This professor is accompanied by a priest, a local boy and two American boys, all searching for religion or gold.
The boys' edition seems to not be rewritten so much as just trimmed. The prologue is gone and from what I compared between the two books the differences are sentences or parts of paragraphs removed entirely with the text that's left apparently the same. Basically just made shorter and faster rather than simplified. The illustrations in the boys' edition are more cartoon-like than the few more realistic drawings in the standard edition. The copyright for the boys edition is five years after the author's death and in the name of his wife - she was a writer herself and most likely made the changes. On the basis of no evidence whatsoever I'd hazard a guess that she needed money.
There must be studies of children's editions though I'm not aware of much commentary about this (as distinct from teaching editions). There of course have always been texts of classics modified for younger readers (at least within reason - probably no kids versions of Suetonius or Rabelais). Children's versions of current books, at least today. are more likely to be ones intended for school or public interest use such as the younger reader editions of I Am Malala and Enrique's Journey. The world was recently given a young adult version of The Da Vinci Code, thirteen years after the original and to no obvious demand. But that's a rarity for fiction.
Thomas Allibone Janvier (1849-1913) was a Philadelphia journalist who traveled through the Southwest and Mexico. When he started writing fiction those experiences provided background. Other books include Stories of Old New Spain, Legends of the City of Mexico and An Embassy to Provence. His niece was Emma Janvier, a Broadway actor who seems to have been fairly well known at the time.