There's certainly plenty of violence in fairy tales - even though so many have been Bowdlerised the gore still pops through, as do those underlying messages about sinister men and so on
Yet we'd think nothing of giving a child a fairy tale to read. Religious texts can also be extremely violent and adult - I used to wonder what on earth the inhabitants of Sodom and Gomorrah had done, as I just couldn't conceptualise it when a kid!
However the most throughly depressing thing I ever read in my life was one of the books in the spare bedroom at my Nan's house. She obviously thought it was OK for a child or she wouldn't have left it there - it was an autobiogrpahy by a ballerina who had survived Polio and lived in an iron lung - complete with gloomy pictures and gloomy cover art (I'll see if I can find it later as I still have it...). I'm a pretty gloomy old curmudgeon...did it damage my childish sunny outlook on life? Would Hurin do the same?