There are some non-critical jobs in the military with flexible hours. That is all well and good for them. There are others who themselves and their families are making a huge sacrifice to protect you and me. My military family member was in and out for months prior to being deployed for 3 months, home for 4 days (work like 6 am to nearly 10 pm) to prepare for being gone for 7 more months. Family Christmas will be in March.
If dad is a member of command - or even enlisted - deployed in the middle of an ocean, it is not possible to take time off, humevac, fly back to home port just to go to an appointment. Or he may be supporting troops in a war zone or thousands of other jobs in the military that are 24/7 every day of the year. There are missed births, birthdays, anniversaries, holidays, and milestone events.
There are many other jobs in the community where individuals cannot take time off whenever they want. There are far more time critical events than taking a child to an appointment that can easily be scheduled and attended by another adult.
Remember this job is paying the bills, and in this world could be the best/highest paying they can get. Would mom be willing to give up the support and benefits dad's job provides or would she demand the same level of financial support?
Having a job that allows you to take time off for your children - or even yourself - is a luxury. Be grateful and support those who are not as fortunate whether they are family or friend.