Baby & Me(1991)

Aka-chan to Boku

Takuya is a normal Japanese elementary student whose mother died not very long ago, leaving him alone with his father and his baby brother Minoru. But his father is a busy man, and Takuya has to look after Minoru. Because of this responsibility that would normally never burden a child of his age, Takuya sometimes resents his fate and his baby brother... but his love for Minoru gives him the strength to carry on.

(Source: Anime News Network)

Notes:
- Includes the one-shot "Time Limit".
- Includes the one-shot "Secret Boy ni Tee Dasuna!!".
- Includes the one-shot "Baka de Karukete Wagamama de".
- Includes the one-shot "Natsu to Kimi no Irradiation".