Completely agree with wtrumpet, - good fiction offers marvellous entertainment, it stretches your imagination, it provides a temporary relief or respite if real life is difficult - no harm in that.
It can inform you about history or people or countries you do not know, all mixed in with the story and in an easier form than a textbook.
Certainly fiction by definition is not "true" but the best and most successful writers are great observers of human nature, of the thoughts and feelings of different people and their actions or reactions and can bring convincing interesting characters to us.
Good literature in any language can expand your vocabulary,and improve your spelling and grammar. Good children's fiction is the perfect enticement to encourage children to read.
Please note use of the "good" - there is a lot of rubbish around, but you can decide for yourself by reading some fiction.