I think All you can do at this stage is be a good and supportive parent.
As a single mum she needs to know that cm is paid on time so she can afford to provide properly for the children. As a new mum, she may want to discuss the new baby – without being pressured over a relationship. As a mum of two she might want the occasional day off and be able to trust you to look after the children safely.
I’ve no idea how your ex feels but I guess you need to build back the basic trust necessary to co-parent before anything else.