HELP ME FIND THIS MANHWA

I'm looking for a manhwa where the main character is a baby girl with grayish-blue hair not dark, more like a soft or muted tone. She has an older brother who’s still a kid, and his hair is either gray or light blue, with bangs. There’s also a very young blonde prince who’s being abused, and I clearly remember that he and the older brother become pen pals at some point, which was a really cute moment. All of the main characters are babies or really young children, and the setting is more on the fantasy or royal side. The story is mostly cute and heartwarming, but it does have some serious moments too.