'A child reads a book smiling.' is currently marked as incorrect, I can find no fault and I believe the sentence makes more sense than the smiling child reads a book. Of course I am English, not American so perhaps in the American form of English children do not smile because they are reading a book, or thinking about something whilst reading a book causing mirth but smile incessantly regardless of whether a book is being read or not.
I answered "The smiling child is reading a book", and it was not accepted. It should have been. The "correct" answer, "The smiling child reads a book" is grammatically incorrect English. You need the present continuous - the -ing form. I should know. I am a native speaker English teacher.