Stephen King comments on people being upset about the child orgy scene in 'IT':

https://www.vulture.com/2017/09/stephen-king-statement-on-child-sex-in-novel-it.html

In the original novel, the group of kids — known as the Losers’ Club — have defeated the manifestation of their nightmares they call “It” (a.k.a. that evil clown). But they get lost in the sewer tunnels after the showdown and start to panic.

The sole girl of the group, Beverly Marsh, tells her male friends that the only way for them to get out of the tunnels is … to have sex with her. What follows is an extended description of Beverly encouraging and having sex with each of the boys. It is, technically speaking, a gang bang featuring children.

A comment from SK's web site from 2013 acknowledged to be from SK himself:

I wasn’t really thinking of the sexual aspect of it. The book dealt with childhood and adulthood –1958 and Grown Ups. The grown ups don’t remember their childhood. None of us remember what we did as children–we think we do, but we don’t remember it as it really happened.

Intuitively, the Losers knew they had to be together again. The sexual act connected childhood and adulthood. It’s another version of the glass tunnel that connects the children’s library and the adult library. Times have changed since I wrote that scene and there is now more sensitivity to those issues.

When asked about this comment on his web site, SK responded:

That sounds like my statement. To it I’d just add that it’s fascinating to me that there has been so much comment about that single sex scene and so little about the multiple child murders. That must mean something, but I’m not sure what.