I was a hard-core night owl for years (all through college and my first 20 years of working). Then I had a kid, then another. They're 10 (+/- a bit) and I now reliably wake up sans-alarm at 5-5:30 every day, after years of doing that for [or because of] the kids. They even sleep later than that now, but I'm easily up by then.

It does mean that I'm tired by 11 or midnight, but even when left entirely on my own schedule (kids away on school vacation), my "new" natural schedule persists.

I didn't seek to change it (and if it drifted back later, I might even be slightly happier).