As a nanny I wouldn't do it if I didn't know the mom very well, however as a mom I wouldn't be very offended by it. I mean, you said the child looked cute, right??

Who can resist an adorable photo of her child no matter what the outlet??!

I would never do that. First off it is in my.contract that I won't share photos of the child with non family members. But even if it wasn't in my contract I wouldn't do it unless I asked the parents. It is rude.

Our nanny occasionally posts photos of my DD on FB but she always asks first. I don't like to be tagged in photos since I don't generally post photos of my DD on social media, and she knows that, but if she did tag me, I wouldn't get angry or anything. I trust my nanny and she has never posted anything I'd be embarrassed to see. Usually, they are photos of them having fun.

I don't see the issue with the wedding dress. Playing dress up is pretty normal. If the MB doesn't care, you shouldn't either.