pictures of kids and social media

So bio mom posted a picture of both her girls in the bath tub up on social media. you can tell they are naked but can't see any parts that shouldn't be shown. however we don't find this appropriate. the girls aren't little babies they are 7/8 years old and to be posting pictures of them naked in the bath just doesn't seem right especially on social media where the picture can get out for anyone to see. SO is unsure how to handle this but thinks he should at least tell her she should take it down because that's not really an appropriate picture of his child. does anyone think that it's ok to post a picture like that and we are just overreacting or should we be concerned about it like we are? edit: only one of the girls is my SO's daughter the other belongs to her step dad who also doesn't agree with the pictures being up on social media. edit: you can tell they are naked and seeing as we have never dealt with this before it doesn't seem right to us at all and don't know if it's legal or not. the father's are more concerned about pervs on the internet getting ahold of the pictures of their daughter's that you can tell are naked in the bathtub.