The known differences that we have between the children are:
the last one is a boy.
the one kept in a cage is a girl.
The dead child-unknown.
I do not believe we can rule out at this time that she got an ultrasound with the girl and the sex of the baby was a reason.
We know the boy was born after the two of them got legally married, but the girl was born before the two of them got legally married. I know it's hard to believe that was the reason for hiding the girl (certainly we are no longer in the 19th century), but I don't think it can be completely ruled out either.
We also don't know for sure who the bio dad is of the children. Potentially that could lead to disparate treatment.
So, there are a few alternative theories for the disparate treatment of the pregnancies and resulting children.
the last one is a boy.
the one kept in a cage is a girl.
The dead child-unknown.
I do not believe we can rule out at this time that she got an ultrasound with the girl and the sex of the baby was a reason.
We know the boy was born after the two of them got legally married, but the girl was born before the two of them got legally married. I know it's hard to believe that was the reason for hiding the girl (certainly we are no longer in the 19th century), but I don't think it can be completely ruled out either.
We also don't know for sure who the bio dad is of the children. Potentially that could lead to disparate treatment.
So, there are a few alternative theories for the disparate treatment of the pregnancies and resulting children.