Re: contact the NSPCC ?? advice
I see where you are coming from but I'm sorry, I don't agree. Countless kids have died because people thought it wasn't their business to interfere. If there are actual threats and the words 'black and blue' being bandied about, personally I would do what Annie and B-Brain have suggested, ring for advice. I know from the other side of things how very hard it is to get Social Care to intervene and take children away, they do not do it lightly. However these children have no voice of their own, We all have a Duty of Care to each other. Apart from anything else, this will be a horrible strain on you until you pass it on. You can ring and ask for advice before disclosing who it is about, ask if they think it is something you ought to formally pass on to them. The family need never know it was you.
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All manner of thing shall be well... (Julian of Norwich)