Boku Wa Ne

Tetsuta’s mother died when he was a small child, and after that his father always came home late from work. It had always been Tetsuta’s wish that his dad would come home early. Then one day his dad anounced that they would be having a new babysitter to take care of them! Tetsuta was strongly against this until he met this beautiful babysitter…
From Baka-Updates:
Tetsuta and Aya are two siblings who lost their mother very early in their lives. Despite being loving and devoted, their father has since buried himself in work and hardly ever spends time with them.
Tetsuta is fully accustomed to looking after his younger sister and cooking for the family, so he vehemently opposes his father’s suggestion of bringing in a helper to tend to matters around the house and care for them. But his attitude changes the moment he meets this beautiful and kind-hearted housekeeper…