In the interview, Cardellini also commented on the actress’ accessibility off camera, due to her charming personality on set. This especially came in handy when it came time for the kids on set to play opposite La Llorona. Although her appearance was one of an evil spirit, because she was so great with the kids on set, they were able to do their job without actually getting scared out of their wits of the actress.
Article source: https://www.cinemablend.com/news/2470573/having-an-actress-playing-la-llorona-on-set-made-a-world-of-difference-to-the-cast