answer: The day after tomorrow is Tom and Mary's birthday. #Person1# and #Person2# will invite all their little friends to come and celebrate.
documents: #Person1#: What's the date today? 
  #Person2#: December the fifteenth. The day after tomorrow is little Tom's birthday. 
  #Person1#: Right . What present should we give him this time? By the way, how old is he? 
  #Person2#: Thirteen today and tomorrow. Fourteen the day after tomorrow. 
  #Person1#: How time flies! He's a big boy now. 
  #Person2#: And don't forget Mary, Tom's twin sister. It's her birthday, too. 
  #Person1#: OK. Let's invite all their little friends to come and celebrate.