I am not walking in your shoes, but if I were, I would set a specific time for her to call the kids. I think she's trying to show that she's a good mother by calling them while they are w/you. Her curiosity is up as to what you are doing with them and if there is another person involved.
Time will tell if she's "fishing" for info through the kids.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.
