But doesn't your theology teach that babies in the womb are pre-determined by God as either elect or reprobate. And this doesn't change?
Perhaps they're not. You don't know and I don't know. But there is nothing in Scripture that says they aren't, and some that says they are.
"I was cast upon thee from the womb: thou art my God from my mother's belly." -- Psalm 22:10
The RCC catechism (1250) says that unless a parent baptizes their infant, those children cannot be a "child of God." --
"The Church and the parents would deny a child the priceless grace of becoming a child of God were they not to confer Baptism shortly after birth.51
So you have the parents electing their child, and not God.
I haven't found any Scripture for that one.