Zongman: The male protagonist of a stranger starts from a child husband

On the evening of April 1st, April Fool's Day, the Kasumigaoka family held a family meeting and announced two things.
The first thing is that my father has to go to Hokkaido for a while because of his job transfer, and my mother will go with him.
The second thing was that the family's youngest son, Dongzhi, was not their biological son. He was found at their doorstep on a winter night fifteen years ago. The couple saw how adorable the child was, and since they had no sons, they adopted him as their own, raising him as a child husband...
ps1: The protagonist traveled through time with his body and turned back into a baby for unknown reasons!
ps2: In the fusion world of Zongman, when your assets and income reach a certain level, you can legally marry multiple wives!