The kids-
Jack Dylan Grazer as Eddie kaspbrak

Finn wolfhard as richie Tozier

Jaeden Martell as bill Denbrough

Wyatt Oleff as Stanley Uris

Jeremy Ray Taylor as ben Hanscom

Chosen Jacobs as Mike Hanlon

Sophia Lillis as Beverley Marsh

And this is what Casey looks like as a child

The Adults-
James Ransone as Eddie kaspbrak

Bill Hader as richie Tozier

James McAvoy as bill Denbrough

Andy Bean as Stanley Uris

Jay Ryan as ben Hanscom

isaiah mustafa as mike Hanlon

Jessica Chastain as Beverly Marsh

Bebe rexha as Casey Williams