I have recently separated from my partner we do shared care with our five children. He has three elder children from a previous relationship aged 18, 17 and 15 who also reside with him full time. Mine and my partner's son who is 7 has behavioural issues which we are sorting help for. But more recently my ex partner left our 7 year old in the care of his 18 and 17 year old children and the 17 year old was asking and screaming at my son to go for a shower but of course my son thought it would be great to be cheeky and pull faces as he does and then took his shoe off and threw it across the lounge room which hit his 17 year old step sister. With that she got up and grabbed him forcefully and threw him into a door frame which resulted in the back of his head being split open which needed 4 sutures and glue aswell. I have already applied for legal aid and family law. I'm also trying my hardest to get a house I have also made plenty of FACS reports previous which also they are finally involved and we have a case worker but my ex is very cunning and manipulative and is turning everything into he said she said which is not working out for me at all. But now yet again my child has been hurt in his care by 1 of his older children my question is legally what can I do to protect my kids whilst in his care untill the legal system finally open their eyes to what their truly like and what they actually do or don't do more so. Any help would be sensational thank you.