A parent slapping their small child very hard in the face in public

I once witnessed a mother very upset and slapping her small child (possibly 4 yr. old) as I was walking out of a store. She hit her child so hard you could hear it just as the child began to scream in pain. My heart went out for this child as prior to being slapped I only heard him being repetitive asking for something as he was being ignored by his parent. Although I do not know the entire story, and understand everyone has their beliefs and forms of discipline how would you react if all?

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      yesterday a child was crying in Walmart and the mother whispered something in the child's ear and the child said "no mommy you are not going to hurt me again" and just last week at Hy-vee I Hurd a child yell stop pinching me mommy it hurts bad and then the mom must have pinched him harder and he just screened and I have probably 2 million other stories to tell you LOL SOOO sad though so sad :-(
        I consider that physical and psychological abuse, not a form of discipline. And I would probably make that parent rather uncomfortable.
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