If you want to have a relationship with her, tell her how you feel and include the children in this... as if things go serious they will become part of your life too.
Let her know that you would prefer to take things slow as of to prevent the mistakes of the past.
Also there’s two children to consider now. The last thing you or her would like to do is that you would built a relationship with the children just to end up in heartache later on, for all of you in the end.
Problems can be worked on if there’s respect for one another, mutual space and love for each other.
Leave your feelings by the door and also ask yourself... what advice would I give to a friend if they found themselves in this situation?
Good luck with whatever you decide.