I agree with you in part. Everyone has their burdens and it is kind to help your fellow man out. Occasionally. This isn't a matter of mom being stuck in between childcare on a couple of bad days.

If this happens more than once a week. I would say that there is a problem. Mom is abusing the hospitality and good will of her coworkers; she isn't getting her work done and keeping others from getting theirs done.

It is an office, not a daycare center. Mom needs to find better alternative childcare or face up to the boss and arrange for a way of keeping her kids out of everyone's hair. Maybe by taking over a conference room or something.

It is good to be compassionate but not a doormat.