I don't recall much, but I read it about a half year ago and it didn’t have many chapters back then. Also it was a historical setting with romance. The story was something like about a first born girl, who was reincarnated or reborn into a noble family, and this family had to protect (or something like that) another noble family. The male lead suspected that she won't be staying on his side; moreover he insulted her during their first meeting. Also, the characters were children.
Might this be I Will Quietly Disappear...?
I was reincarnated. I was reincarnated into a ducal military household that held the protection of the country on its shoulders. I, who had possessed clairvoyance, saw a fragmentary future. Thus I knew that I possessed no combat prowess. It was my younger brother who had, and because of that, there would create an unnecessary fight for successor. “If I don’t have it then it can’t be helped,” before any needless conflict arise, I thought to run away from home, but…
A high school girl living in Japan is reborn in another world as Princess Luce, a young girl and a member of the Listyl House, who're responsible for protecting the royal family of the Asteria Kingdom. One day, her father takes her to meet Prince Rasmere, who is also very young. His intial reaction upon seeing Luce is rather frosty, to say the least.
This manga currently has just six chapters.