I haven't read House of Hades,
I learned last night from Twitter that Nico, a boy character in the Heroes of Olympus series, is revealed to have a crush on Percy Jackson. The book has been out since October 8th, and it's been very much on the radar as the latest in what's arguably the most popular middle-grade series out there (not that Wimpy Kid's having terribly hard luck). I've now seen several online references to this particular plot point, but I've seen them all in the past twenty-four hours. I don't claim to have seen every response out there, but my sense is that this very mainstream book has been out there for a month without becoming known as a "gay book." As an astute commenter said on my last post, "we should be normalizing queerness so that it's not 'inappropriate' for younger readers." That's exactly what Rick Riordan has done here. A boy has a crush on another boy just as he might on a girl, and he's understandably conflicted about it (the world doesn't necessarily make it easy), but there's nothing graphic or "dirty" about it.
With previous middle-grade titles, I've felt some need to mention the presence of homosexuality to parents shopping for particularly young readers, simply because that presence has been somewhat unusual and unexpected, and it's reasonable for parents to want to be prepared if questions come up. But I feel this book may be a turning point. Nico's existence makes the presence of gay characters in middle-grade much less unusual, much less noteworthy.
Thank you, Rick Riordan.