Thank you for confirming that.
If you are concerned that your children would be at risk of harm in the other parent's care and there is a risk that they will try and remove them from your care if contact is not agreed in the future, you could consider applying for a) a specific issue order for them to be returned to you and b) for a prohibited steps order to prevent your children being removed from your care without your agreement in the future. For this type of application
You would apply on a c100 form, here:
You send 3 copies of this form to the local family court centre.
Alternatively, you can apply online:
It would be an urgent application, so you would tick that exemption from the mediation requirement. You'll need to complete section 6 of the form as to why it is urgent, here you can reference the concerns social services have shared with you.
The application costs £232.00, and you can represent yourself so you don't need to engage a lawyer. You can also possibly get a fee exemption if you are on low income/have low savings.
For this you would need to fill out a fee exemption form: http://www.gov.uk/get-help-with-court-fees
I hope that this helps you today?