Just wanted to check that I have done the right thing, we had stopped at a McDonald's while on our way home from holiday when I saw another mother slap her child across the face (yes, she was being difficult). I waited for my sister to come back and we loaded our children in the car and I went back in to where they were sitting and said, very non-confrontationally, that I knew it wasn't my place but it is never acceptable to slap a child on the face no matter how frustrating they are being and that she was very lucky that I didn't call the police. She responded, very eloquently, with 'f--- off' so I said that I would call the police and left (I had the licence plate of their vehicle). The police advised that they would do a welfare check on the child.
Did I overstep the mark and will the police actually do a check?