Trying to help with non-work-related things directly is a minefield, but ensuring that the employee has access to everything they need to succeed should be table stakes.
But job-related stress is there and is often solvable (e.g., a developer may be stressed if he committed to a a week's worth of work done in 2 days, etc.). My 2c.
Flexible work hours, remote work and a strictly never-over-40-hours work week has been absolutely essential to be able to cope and still be a good parent (hockey practice weekdays at 4 twice a week for example).
Solving stress out of work is not reasonable. But knowing about it and being flexible is. One key reason to understand this is that many people recommend vacations to people who are stressed. If stress is coming from outside then this has a negative effect and work may be an escape from whatever other issues.
As a manager I’d consider tools to use might include paid time off, temporary re-assignment to work that is more rewarding/less demanding.
Even simple things like showing concern by following up to find out how those life stresses are coming along and being an ear to listen can go a long way.
Some of it could be "solvable" (better pay, better hours, ...), but some of it may not (family problems, health issues, ...).
Is it taken into account or addressed?