I hate to be the person thats is all like "as a parent...", however - to me having to leave early, come in late or take a day off to deal with kids being sick, appointments or just daycare/school drop off/pickup is worse.
The premise of this feels like "smokers get a break so why shouldnt we?". But realistically my work is still there, i am stressed about the thing i havent done that should/needed to be done that day, the amount of work i now have to catch up on and the extra stress of trying to get the 'non-work' things done as quickly as possible so i can be back at work to get through my workload.
And ontop of that, you likely had to cut your work time short because your kid is sick or hurt and you are also stressed about that, its not like you jump in your car and start whistling to the radio heading home early.
So yes, i think a non-parent should have just as much flexibility as a parent, but thats a conversation to have with your boss and not some guilt you try saddle on parents when they cant be at their workplace for their full X-hours per day. I would never make a coworker feel guilty because they left half an hour early a couple days per week to go like practice for their sport or hobby or something, so afford the same respect for someone who has 'child commitments' instead of your 'leisure commitments' because they arent the ones saying you cant take time off too.