While I surely agree that forgoing kids is a good way to boost your chance of retiring early, that wasn't my thought process in my journey to ER 11 years ago.
I knew at age 20 that I would be childfree, that I had no interest whatsoever in having kids. I was still in college, 2 years away from working full-time. I was also 15 years away from seeing ER appear on my radar, when I paid off my mortgage at age 35. Even then, at 35, I was still nearly 10 years away from realizing that ER was a strong possibility by age 45.
For me, it wasn't, "I want to retire early, so what can I do to make that happen?" Instead, it was, "Wow, being childfree, a choice I made years ago because I had no interest whatsoever in being a parent, has been making me wealthy. I hate my commute and it is increasing the dislike of my job and need to do something big about it. Working part-time has been okay at times but it is not nearly enough. Let's marry these two things and see if I can parlay them into being able to retire early." And I did.