I think I understand why people don't--kids are a sensitive issue. But I'll take marriage advice from single people, and financial advice from pretty much anyone who isn't a Nigerian prince, so I also don't automatically discount good wisdom nuggets from the childfree. Especially these ones:
1. Nannies and Childcare Workers
These people know what's up for real. I realized that my parenting "bag of tricks" was dismally small once I met a girl five years younger than me with no kids who could potty train a child in two months flat and was dubbed the "toddler whisperer" for the way she soothed the savage beasties that we cared for.
I trust doctors. They're smarter than me, and if my kid likes you, I like you too.
3. Childfree Aunties
Whether they're related to you or not, if the childfree auntie (or uncle) has truthbombs to drop than you must heed. Odds are, your child will end up listening to and essentially liking them more than you anyway, so...
4. People Who Hate Kids
Hang on one second. If you find kid-haters distasteful, think of it this way: consider their entire personalities the advice you should be taking. If they are truly scummy and rude, try and do everything in your power to make sure that your kids don't end up like them.
5. Other Kids
My friend's five-year-old didn't have children when she told me that my freshly dyed hair was probably what was freaking my own toddler out. "She's probably scared cause you look like a stranger". Wise words, little one. Wise, indeed.
6. My One Friend Who Can Turn Dookie To Gold
I have another friend who has no children and no plans to, but everything she touches turns to glittery unicorn farts; her career, her relationship, her hair...I will take all of the advice from this person. ALL OF IT.
Like childcare workers, even childfree teachers know more about kids than you can ever hope to. And if they're like most teachers, they are directly invested in the welfare and success of your child, uterine history notwithstanding.
8. Cartoon Characters
I will rip advice straight off of cartoon characters, because at this age, my child already finds Princess Celestia more relatable than I can ever hope to be. So when Jake from Adventure Time says, "Sucking at something is the first step to being sorta good at something." I will repeat it both as parenting advice for myself and for serious life advice for my kid.
9. Pet Parents
I know I said that pets aren't children, but I'm back pedaling just enough to say that we can learn a lot from the people who can teach their loved ones to poop on command.
10. Really, Pretty Much Anyone Who Isn't A Dick
Honestly, this is at the core of any advice that I accept from someone. I consider tone, content, intent, and who the person is. Are they arrogant, snitty, and judgy? If you tell me that the best way to handle an asthma attack is with a tincture of donkey piss and mint leaves, I'm ignoring you. If you tell me that I can get my kid to stop whining by paddling her roundly, I'm ignoring you. Pretty much anything ridiculous or shitty I'm ignoring. Anything misguided but kind I'm forgiving.
Anything with even the remotest chance of helping me out I'm following, whether or not you've pooped out a baby, so lay it on me.