"you Don't Have Kids So You Wouldn't Know"Urgh. I hate it when people say this. Yes, I can appreciate that having kids does give you extra insight... But I don't believe that simply giving birth or taking custody of children, or even legally being considered the "parent" means that you suddenly know exactly how to care for children. After all, if this were true there would be no need for social services in some situations.
Another example - some women will attempt to breastfeed believing that they know all there is to it... Often this is unsuccessful and many people give up. This is where a lactation consultant comes in... Somebody who is an "expert" if you like, with breastfeeding. Chances of a successful and happy breastfeeding experience increase when seeing a lactation consultant....
So my point is, having children does not mean you know how to parent.
I think parents run into trouble when they assume they know it all. Advice from others is taken with offence. I've seen this so many times.