If one has a child with a woman, and not married to them is it permissable for them to be alone with one another (not being married at the time of conception or after the birth) The 3rd party will always be shayton, and are children suitable chaparones.

Praise be to Allaah. 

We put this
question to Shaykh ‘Abd-Allaah ibn Jibreen, who replied:

 They
will no longer be counted as being alone together (khulwah)
if there is a third person present with them, whether he is their child or
someone else’s, and whether he is the child of zinaa or the child of a
legitimate marriage – on the condition that he is above the age of
discretion and is of sound mind, that there is no fear of fitnah, and that
the woman is wearing full hijaab.