In the UK, you (a person who is aware of child abuse allegations) can always contact the social services and have a confidential conversation with them about your concerns.
I have done this when I believed there may have been child abuse (in one case possible serious neglect, in another two cases - involving allegations of child abuse). In the UK the Social Services will listen confidentially and they can act to get (in an emergency) even without prior police or court involvement.
Also if it is a case of possible sexual child abuse they will often discuss your options in a reasonable way. If what you tell them is serious enough in their opinion then they can go to the police and importantly they can get court orders, safeguard children, remove children without having a conviction in court which may never even happen.
I have sat with social services staff to provide information and ask advice on three separate occasions and I have been to the police in two of those cases after a discussion with them. One case I went to the police because I had evidence of child abuse available to "help them with an investigation". In another I had simply an opinion that someone (a jw) was being fitted up by a spouse (also a jw) eager for a more favourable divorce.
So I have never been afraid of the social services or the police and after a couple of dealings with the (anonymous idiot wankers - sorry was that unprofessional of me?) "brothers" on the service desk I simply ignored them as they hmmmmed and haaaaawed and tried to dissuade me from imparting information to the proper authorities.