This is about babysitting the boy's niece and then his classmate found out about it and ask her to help him babysit the child because she somehow resemble his sister; the mother of the child. And as the story goes by, they start to fall in love with each other.

The other one is about babysitting also where they are neighbors and the child says that she is from the future.

And the last one is about a child left in front of the house with a note saying he is your child

The first one might be: Junjou Drop but I'm not too sure...

The second one might be one of these:
Papa to Mama Hajimemashita.
Renai@Home part of the Koakuma Lion volume- I think it's this one, but again I'm not sure

Thank you! Can i ask for two more mangas? It is about having a strict father over protective to his princess preventing this guy to make a move on his daughter but the guy proved his love for the girl that is why he gained the trust and blessing of the father.

The other one is a one shot about the girl moved to the country side where an annoying neighbor is there. Then she met a boy and fell in love with him. She confessed to him that she wanted to marry him and kissed him but eventually he is a ghost. That moment was raining when the ghost boy vanished the annoying neighbor came to her rescue. On the day of their wedding, it was raining and she asked her mother what was the name of her father...... I think the ghost was her father because when she was young, she kept saying that she will marry papa.