Is it ok to post pictures of other people's kids on the internet?

Yesterday I ended up in a conversation with a stranger on Facebook in which she said that she took pictures of her kids and their friends at events like her kids' birthday parties and posted them on Facebook for her friends to see.

I was gobsmacked that she'd assume that it was ok to post pictures of other peoples' kids without their permission. She replied that she posted them to "Friends only" so it was fine because she knew everyone who was seeing those photos.

But what about the fact that the kids whose faces are in those photos (and the parents of those kids) don't know all the people who can see them?

She said that if I objected to having photos of my kids up on Facebook I could let the parents know and the parents would have the choice of whether or not to invite my kids to their birthday parties.

I'm stunned by all of this. It would never in a million years occur to me that someone else would put a photo of my kids on their Facebook page without my permission, or would act as if I was infringing on their rights by asking not to have pictures of my kids on Facebook.

I don't even know how to assess this situation. Am I extraordinarily conservative? Or is she taking extreme liberties?