In my opinion Byul is a like a far second like he was once a close second but when Rourou recited the phone number he became the supreme baby JankenIku
Oh god exactly! He's cute and smart! Such a good kid who isn't too mature for his age (unlike how other mangas depict smart kids)
Of all the yaoi/shounen ai that i have read, rourou is by far the cutest baby!! Not even the babies in omegaverse could surpass him!