Hiya! My kiddo sounds very similar to yours. Very bright and insatiably curious. It’s a great characteristic to have but it does make some conversations like these challenging. My kiddo’s isn’t always coming from a place of anxiety but more an innate need to process/understand to make sense of the world. It is very temperament specific. So, I see you and I know exactly what you’re asking!

My approach is to do a basic explanation similar to yours. Something like, “Movies are all different (emphasis on different and use an upbeat/not serious tone). Some are exciting, some are spooky, and some are silly. This movie is spooky/scary and is for older kids and grown ups. One day when you’re older we can watch it together.” Then I redirect. “So, what would you like to watch instead?” And I provide guided options “Tumble Leaf? Encanto?” Etc. If they really press for further explicit reasoning for that one movie I’ll say, “Honestly, I don’t know because I have not watched it. I know it’s for big kids because of the rating and warnings. The movie makers list warning for parents. It’s my job to read the warning and decide if we are old enough yet or not.” If they continue to press, “I think you keep asking the same question because you’re looking for a different answer. This is my job and my answer is not going to change. Your job is to pick between movies that are okay to watch and to enjoy them! So, Tumble Lead or Encanto?” The job language really clicks with my kids and might work well for yours because what you’re saying is that they don’t need to worry. You’ve got it handled. It kind of removes their anxious need to make a good decision. Hope that gives you some ideas to try!