There is not an official number but there is the famous Five Word Rule. It states that if 5 consecutive words are used as someone else wrote them then it can be considered to be plagiarism even though you might not have wanted to plagiarize and genuinely had the same thought.
Not sure what story youre asking about. would be helpful if you gave a little more info :)
C) the mom may not be at home or somewhere else the child couldn't find her, so maybe getting an ice pack while searching for the mother will be a choice
