In an ideal world parents would consider their neighbours when they live in a flat/terraced house and have a crying baby, noise insulate where possible, have carpets/rugs instead of hard floors, have the baby in the room in the house that least disturbs NDN etc.
In an ideal world neighbours would feel confident parents are considerate, aware of their surroundings and are doing all they can to keep noise as low as possible. They then will be sympathetic to a baby crying in the early weeks/months and maybe make some temporary adjustments (wear earplugs, move to spare room if either is possible) to support the new parents.
In an ideal world if the noise nuisance continued beyond those early months a neighbour would be able to amicably say it is impacting them and the parents would apologise, listen and see if there was anything they could do to help reduce the noise disturbance and let the neighbour know what they are trying/ask if there is any improvement.
Unfortunately we live in a world where everyone, including parents, are too self-centric and don't even try to see another persons circumstances.