Kids at R rated movies.

The hubby and I went to see The First Omen rated R at Landmark yesterday and this couple brought their kids! Two girls about 8 and 5. Honestly ruined the movie for me knowing they were seeing what I was watching. I only noticed there was a child in the theatre cuz when Spiderman appeared during the previews, the youngest one yelled out "'piderman!". Not sure if any of you have seen the movie, but it is horrifying to know children saw that kind of content. Is this normal here, cuz there's a few times I've been to movies where people brought young kids or infants to films they shouldn't be seeing, or in the infant situations, loud crazy action movies that made the baby cry. Maybe people don't think it's a problem here?