The only way to make a good and shocking Exorcist movie
Hire an 18-year-old actress who looks like a 14-year-old girl so she can say vulgarities and perform scenes of sexual nature (in 1973 there were no laws protecting children or access to psychologists on the set, it was the only way they could expose a minor to all those type of scenes)
Another less plausible way: hire an adult actress and, thanks to digital rejuvenation, turn her into a little girl.
When I imagine an exorcist movie, I imagine this: shocking, violent scenes, scenes that cause discomfort, disgust, etc
If they continue hiring children, all that will be limited