As of House of Hades, he has blindsided everyone by adding an LGBT character to the Percy Jackson/Heroes of Olympus canon in the form of Nico di Angelo, who has his hidden crush on Percy dragged out of him by Cupid in front of Jason. IN A CHILDREN'S SERIES. PUBLISHED IN PART BY DISNEY.
His statement regarding this on his website's FAQ, in particular:
"I am committed to writing appropriate books for the middle grades. This means no bad language, no gratuitous or explicit violence, and no sexual content beyond what you might find in a PG-rated movie – expressions of who likes whom, holding hands, and perhaps the occasional kiss. The idea that we should treat sexual orientation itself as an adults-only topic, however, is absurd. Non-heterosexual children exist. To pretend they do not, to fail to recognize that they have needs for support and validation like any child, would be bad teaching, bad writing, and bad citizenship."