I am a Sw. Have you only been interviewed by social workers? Have the police spoken to you?
In situations of allegations of childabuse a joint investigation is carried out. In registry the police lead the investigation. The CPS ultimately decide whether there is sufficient evidence to prosecute.
What I would have expected to happen so far is this...
You phone police. Police contact children's services and undertake a joint visit to the family. Children are taken to local hospital for a medical to identify and record any injuries. Photographs to be taken by police photographer of the injuries. Parents and children are all spoken to individually to see what they have to say about home and any injuries the children have. Strategy meeting held to determine if children are at immediate risk (if they have injuries there is very little doubt). Children n are placed in a place of safety (either with family, friends or as a last resort foster carers). Investigation into the allegations and injuries continues and an Initial Child Protection Conference is held.
The onus is on the police to investigate the criminality and the CPS will decide if they have enough evidence to go bring criminal charges.
Even without sufficient evidence (not unusual in allegations of child busy as often it's a childs word against and adults, and children are 'unreliable witness's, however, in this case it's an adults word so evidence is much stronger) children's services can request a judge to make a finding of the liklihood that the parents are responsible for the injuries. They can also carry out assessments of parenting capacity and if it's felt the children would be at risk if returned to arrests care they will seek care orders to ensure the children are cared for elsewhere until they reach adulthood.
You should.be exceptionally proud of yourself OP. Even if no criminal charges are brought, you have done a rare thing indeed. You have sacrificed your own comfort to protect a child. People like you save the lives of children who would otherwise die one day when their finally goes too far and hots them so hard they can't recover.
Perhaps there were earlier opportunities, but it is not easy to be the one who stands up and sometimes it's hard to know what is a physical chastisement and what is abuse. The important things that you have acted now. So be proud and don't doubt yourself.