I hesitated to post this OP because I really hope it doesn't make you feel worse, but please bear with me, it gets better at the end!
I was abused as a child. Beaten, shouted at, thrown across the room, starved and deliberately dehydrated. My dad was the main abuser (but mum did absolutely fuck all to protect me or my brother, so I hold her almost as culpable) and he was so confident in himself that he didn't care who saw, because no-one at all stopped him. Not a neighbour, relative, parents' friends, passers by or even a teacher.
Until one day when I was about 8. My mum's old boss had dropped in at the house for something (the rest of us hadn't met him before) and while he was there I got screamed at and punched in the head by my dad, right in front of this stranger.
The man leapt up, grabbed my dad's arm and shouted "that's enough!". My dad was furious, but of course he wasn't going to take on another grown man so he walked out of the room - I think he went out to the garden - and I ran to my bedroom.
I won't lie, I knew I would suffer for that later (and I did) but honestly just that one person showing me that this was NOT normal and NOT acceptable saved me. I held on to that thought for years.
So, long story short - yes, there is a chance that the woman would be even angrier with the little boy, but if his life is anything like mine was, he now knows that he is not worthless and someone does care. And FWIW I've done exactly the same in your situation too.
(And please don't worry about me now, the abuse stopped when I was about 16, I met my wonderful DH when I was 18 and it's our 40th wedding anniversary shortly. We are both peaceful, gentle people who absolutely adore each other. We don't have DC but have filled our house with a variety of pets, mostly rescues, nearly all a bit wonky and they bring us so much joy. We have a fantastic life.)