Baby, Kokoro no Mama ni!

19-year-old Roji Shizuru has a crush on a fellow university student, Nana, but there always seems to be complications when he tries to get closer to her. For one thing, he's afraid his hot friend Tachibana Masaki will steal her. Beyond that, the main complication comes from the interference of children, specifically one odd child called Maida Kokoro, who keeps clinging to Shizuru and calling him "mama."

(Source: MangaHelpers)