A lot of us were born in places that are no longer economically relevant. The retired are less geographically restrained - I wonder why they don’t more often follow their adult children. For example some of my Chinese coworkers don’t need to go back to China for childcare; their parents and in-laws rotate shifts here.
Also keep in mind, if both generations have kids at 30 (or even younger in a more traditional setting), grandparents are also still working age when the child is born.
That's fair, but the way I've seen this done is with a 2-bedroom apartment. A young family will need that eventually anyway. The second bedroom can be the caregiver's until it becomes the child's.
Also keep in mind, if both generations have kids at 30 (or even younger in a more traditional setting), grandparents are also still working age when the child is born.