Should you tell other parents if you see them doing something 'wrong'?

[Nessalina]

I know that a heck of a lot of parenting is opinion rather than fact, but there are some things are are pretty much universally agreed on, and as a first time mum I think I'd want to know if I was doing something I shouldn't...

One of my fellow NCT mums has a 9 week old, and from a very early age (3 weeks) she has hardly supported his head at all, she sort of sits him up slumped on her knee, and I felt very uneasy about his neck not being supported but didn't feel like I knew her well enough to butt in. Now he's 9 weeks and she's posted a pic on Facebook of him forward-facing in a carrier, which I know is contentious either way, but surely definitely not recommended til 4 months at the earliest! But I still feel like I should probably just butt out, despite maternal instinct on overdrive...

So is it EVER ok to point out a parenting mistake? Would you want to know if it was you?

Demented my dd's head and body are "in proportion" for her age. She is of an age where she'll object if you don't let her sit and play, have full tummy time etc.

Um yes, if you see someone shaking a baby, I think you should say something. Correct me if I'm wrong, but never heard of a baby suffering shaken baby syndrome or anything else from the lack of a parent's hand at the back of the head during normal everyday care.