Daisuki!! Yuzu no Kosodate Nikki

Yuzu, a 26-year-old mentally disabled woman with the mind of an 8-year-old, falls in love with Sosuke, a man with a similar disability. After Sosuke is involved in a fatal accident, Yuzu's family discovers she is 5 months pregnant with his child. Though Yuzu is intent on having the child, her mother, Miyoko, is immediately against it. After her family comes to terms with her pregnancy, Yuzu eventually gives birth to her daughter, Himawari. With many odds against her, Yuzu does her best to care for the daughter she so dearly loves.

(from mangaupdates)