Thank you for your question
My name is Clare
I shall do my best to help you but I need some further informtaion first
how old are the children
What has the pattern of contact been until now?
At the moment there are no court orders in place - it is just that since the children live with mum she has the physical ability to prevent him seeing them.
She has lied to Social Services - and clearly they have to assume those lies might be true - that is why they have said no contact until matters have been investigated.
The way forward is for your son to apply to the Courts for an Order allowing him to see the children.
There will then have to be a proper investigation of any allegations and the family court will also consider whether or not his son is safe in the care of his mother
I hope that this is of assistance - please ask if you need further details