This I agree with (mostly). As an employee and an employer, this is how I treat things. I expect those without kids to plan their flexibility with a bit more foresight, as "oh shit" timing happens a lot less. But if there is conflict due to a preplanned flexibility and a parent's emergent issue with a child, the business deals with it, that's life. The. if an employee who was using flexible time can help out, all the better, but not required.

I know I'm not the norm as a business leader, and have had conflicts about that with other less accommodating leaders in the past, but that's how things should be. Flexibility is a priveledge, and a requirement, for the business and employees alike.