en_tn_lite_do_not_use/isa/49/20.md

The children born during the time of your bereavement

Yahweh speaks of the time when the people of Jerusalem were in exile as if the city was bereaved of her children. Those who were born while the people were in exile are spoken of as the city's children. Alternate translation: "Those who will inhabit you, who were born while the people were in exile" (See: rc://en/ta/man/jit/figs-metaphor)

The place is too cramped for us

This means that there will be so many people that the city will be too small for them all to live in it.