Home Alone

Karamatsu has turned into a child. (Make your own age up based on his behaviour)
This is very self indulgent. Love seeing a baby Kara or Kara being a big bro to baby bro (need to write something like sometimes yay) And of course this will have Kara Angst (but I assure you, he will be happy)
This is on AO3
Alternative reality kinda of this adorable fanfic. Baby on Board by nakadoo.
http://archiveofourown.org/works/6870745/chapters/15678625
Just too cute!