That all goes out the window once you have kids though. You can't plan diaper blowouts, motion sickness induced car cleanup, meltdowns, suddenly needing endless snacks, ripping off all their clothes and refusing to get dressed, hiding their shoes, hiding your shoes, hiding your keys, napping late, napping early, ...... I could go on.
But then you're likely meeting up with other parents, and they get it, too. So it's not a big deal again. When a parent says they'll be there (with kiddos), they'll likely be somewhere between on time and an hour late.
Being a parent is irrelevant. All you have to do is text and say sorry this happened, be proactive not reactive. Something makes you late? Warn people you'll be late so they can get started without waiting around for you.
A couple of my friends are really bad about this. It's like wasting my time is a sport to them lol. No part of me wants to kick them repeatedly in the shins for being 2 hours late to something for eternity. No part at all...
We had one person in my friend group who was exactly 30mins late every time. Whenever we would make plans we would pretend to meet 30mins earlier to “offset” the lateness. It never worked bc whenever we would do this they would show up an hour after the fake planned time which meant they were still exactly 30mins late to the real start time.
Just ignore their arrival when this happens. They probably enjoy being center of attention for a bit when they show up, if you just carry on like they were always there, it'll probably stop.