well i dont want to think that sarada was karin child but that scene has doubt me
but in here,Sakura seems pregnant ain't she? http://www.mangago.zone/read-manga/naruto_gaiden_the_seventh_hokage_and_the_scarlet_spring_month/md/naruto-gaiden-the-seventh-hokage/5/10/
Hmm... I don't think it's about Karin after all. Maybe the two of them (Sakura and Sasuke) feeling regret after making their daughter having a doubt on them and got the problem with the creepy onion thing, so they just wanna fixed all things then tell her properly about what actually happened in their family (it's come after I've read the first and second row of panels). Even Sasuke was far for being romantic, I guess he want to say that both of Sakura and Sarada are being an important part of his life.
for me, it's make sense.. I feel it too when I read that page, maybe they just feeling guilty for making Sarada feeling confused about her family. I hope there's a scene when Sasuke said that he want protect both Sakura and Sarada ヾ(☆▽☆)
In this part
http://www.mangago.zone/read-manga/naruto_gaiden_the_seventh_hokage_and_the_scarlet_spring_month/md/naruto-gaiden-the-seventh-hokage/6/15/
I wonder of what Sasuke really want to say to Sakura and Sarada in their meeting