Thank you for your question. I look forward to working with you to provide you the information you are seeking for educational purposes only.
Legally, this is something that comes up frequently. Under the law, child protection
and law enforcement do not have to allow a parent or guardian to be present when interviewing a minor. You have a right to get an attorney for the child to represent the child and protect his rights, but under law there is no right for a parent or guardian to be present, which is something many parents and guardians take issue with but is not unlawful.
One of the grossly negligent and incompetent and abusive tactics used by these alleged child advocates is to badger children to force them to say whatever these social workers want to hear (which is why getting an attorney for the child is so beneficial, because an attorney being present stops them from doing this). Just like the McMartin Daycare case proved, these social workers can get children to make false statements all to easily and these statements are not reliable.
So at this point, you need to get your grandson legal representation and they need to file in court to suppress the statements of the child as being manipulated and taken under duress and present these abusive tactics to the court. In addition, once the case is over, you could pursue suit against these social workers for violation of the child's civil rights and for intentional infliction of emotional distress for badgering the child to say what they wanted the child to say and seek money damages against the biased social workers and your son in law, once the case is over and charges are dismissed can also sue them for malicious prosecution.
These are the available options.