With strangers or acquaintences: Unless the child is being physically abused, emotionally abused, and/or neglected, it’s none of your business. And then, you contact Child Protective Services. With friends and family: It really depends on your relationship with the parents. I have certainly made suggestions or shared best-practices with my nephew, cousin, and a few friends. But I was confident my ideas would be considered despite being unsolicited. If they are open to further discussion past my initial suggestion, I’ll continue along. However, if they shut down the communication or make it clear my advice is unwelcome, I let it go.