This is a great case study to explore for getting to grips with how producers and distributors set out to target a wide audience (sometimes it's very niche, but not in this case).
Consider elements that might appeal to an underage audience (young characters: U+G identification); the usual core teen-20-something (15-24 with likelihood of some younger is common); mature adults - old school King fans or of the original movie; both genders... Consider how the King brand, It as a franchise, clown iconography, teasing costume design (and the moody lighting was also part of this, denoting a serious tone) through social media ... great case study!
Kingsman: The Golden Circle spies an opportunity at the UK box office – and grabs It https://www.theguardian.com/film/2017/sep/26/kingsman-the-golden-circle-uk-box-office-it-stephen-king-film?CMP=Share_AndroidApp_Blogger
Dropping 53% in its third frame, the Stephen King adaptation It added another £2.85m at the weekend, taking the 17-day tally to £26.5m. That’s the highest ever gross for a horror film in the UK, unless you – perversely – count the supernatural Twilight franchise. It is the 11th-biggest hit of 2017 in the UK, behind Beauty and the Beast, Dunkirk, Despicable Me 3, Guardians of the Galaxy Vol 2, Spider-Man: Homecoming, La La Land, Fast & Furious 8, Sing, The Boss Baby and The Lego Batman Movie. It should overtake at least half of those titles by the end of its run. The film covers events in the first half of King’s book and a sequel, covering events occurring 27 years later, has been announced for September 2019.