|Why assume Henrietta is Peter & Olivia's only child? Didn't the blue side develop amber technology when they thought their universe was breaking down like the red universe? It the episode with the apartment building where the woman thought she was talking with her dead husband.|
The assumption was based on the timing as seen in the opening credits when the year was given (2015) and it was stated to be the year the Observers took over and confirmed when Henrietta spoke on the last time she saw her parents. Also, the blue universe never developed amber as they never fully understood its technology.