"Your child is reading my book."
Translation:Dit barn læser min bog.
I think it's because it child not children (plural) dit= et words (singular) din=en words (singular) dine=plural words
because the possessive pronoun (he, she, her e.c.t) agrees with child not book, and child is et barn (Et word) you would use dit. You would use Dine if it were children because its plural!
Hope this helps... someone feel free to correct me if i'm wrong!