Speaking as a manager and a direct and indirect boss of a reasonably large (~100 FTEs) workforce:
Yes, PP are right in the sense that it's a management problem.
However, you are also not wrong to think this sounds unfair to you and other working parents.
In my experience, parents - as employees - are really no different from other adults on the whole: you'll have your workaholics where, as a boss, you eventually end up stepping in to force them to take some time off (and may sometimes learn they view work as an escape from family life in the process). You have your chancers, who always end up somehow not being able to cover Helen's long weekend after all (despite having volunteered to), needing several weeks off totally outside of the annual holiday plan after all, or only being able to join remotely (despite several weeks of prep and lead time) after all - "because children". And you have everything in between!
As an executive (read: manager of managers), whenever I end up having to play arbitration judge, I try my best (but, I guess, don't always succeed) to do justice to everyone while also encouraging sustainable operations:
I won't have employees miss out on a child's milestone event because of work - but also: I won't have one parent take half a day off for an assembly every other week with another taking 10 minutes to phone home on a business trip due to a child's 10th birthday (both real, I'm afraid! On the same team, too!) if I can prevent it.
But, as always: fortune favours the bold! In my role, I know about the issues of people who bring them up! So go speak to your management!
PS: I've not even touched upon "parents vs child free employees" - that's another can of worms entirely, but I absolutely have cracked down on "Gemma - for the third year running - does the fiscal year closure on her own with no support because everyone else has kids".