"Don't cry, we should be happy to have a family reunion!" Fang Mujin quietly consoled, while Su Nuannuan hesitated and feared, slowly stopped the tears.

is right. It's not her child. What's she crying about?

Fang Chengzhe told her that she had helped Fang Mujin give birth to a boy, but did not say that she had helped him give birth to a daughter.

So the girl must have been left by Fang Mujin's ex-wife. The big boy in the next room is about the same size.

As for why the little girl saw herself so close, she probably saw that they had no mummy before, and it was good...