However, while filming IT Chapter 2, it seems that Pennywise was quite capable of freaking out a bunch of adults., as James McAvoy recently admitted that the clown really got to him on the set.
The first IT was a massive horror movie hit and made pretty much everybody afraid of clowns.
Pennywise, as played by Bill Skarsgard, was a truly disturbing creation and anybody would completely understand why a bunch of kids would be terrified of him.