Should children star in films not suitable for children?

It is immoral to put a child actor in an adult-level movie, such as horror movies that involve lots of murder? Consider the R-rated horror movie "Child's Play," starring a child actor battling a homicidal doll. Is it wrong to expose the child actor to that kind of horror, or is there a potentially proper way to handle it? Additionally, isn't it a double-standard to have it a practice of having young actors starring in these movies, yet to consider these same movies unfit for children to watch?