DP has a DS from a previous relationship. His partner at the time chose to end the relationship as soon as she found out she was pregnant on the basis that she 'no longer liked DP'. Although DP had some contact with his DS during his early years this eventually stopped due to DS's mother being repeatedly obstructive regarding contact. We do not know what reasons she has given DS regarding the ending of their relationship or contact or what else she might have told him true or otherwise.
DP and I now have 2 children together aged 2 and 4 and I am aware that at some point DP's DS1 may make contact. I am wondering how to introduce his existence to our 2 young children and how to deal with the possibility of contact from him in the future.
I would be grateful for any advice.