Have you ever intervened when someone's been abusive to a child in public?

[MonChoufleur123]

Today at ASDA a guy was shopping with his (I'm assuming) two kids - a boy and girl looking about five and six. I heard him shout 'What's wrong with you now?' at the little boy who burst into tears. Then he shouted at the girl for putting her drink down, then at the boy again for riding his bike too fast outside. He just seemed really angry and they seemed scared of him. They didn't seem like they were misbehaving to me but I know I only saw them for a few minutes.
I wanted to say something, but what? I feel really bad now that I didn't but I don't know how to approach it. Have you ever intervened in a situation like this? What did you do? Any advice/thoughts welcome...

I did once, years ago in McDonalds. A woman was sitting near me with a small child who she was telling off for not eating fast enough and she started repeatedly slamming the child's face into the table/food. I went over and told her she couldn't do that, etc. She got really aggressive and squared up to me, physically threatened me and backed me out of the restaurant. I thought she was going to pull a knife tbh. The staff and everyone else turned a blind eye ☹️ It really shook me up, but I couldn't ignore it.