Imagination is vital to a child's development and when I was a child I read a lot and listened to plays on the radio and 'saw' it all in my mind - as I still do. There was scary stuff too like The Day of the Triffids which I remember but they say a certain amount of scary stuff is also good for kids - some of the so-called fairy stories are quite dark. But 'fearful imaginings' are a different matter and have no place in the lives of Christians.We tend to imagine what we can accept or handle.
However, I have to admit, I have met people who have almost scared themselves to death through fearful imaginings.