"The children are both doing great and there is no need for us to talk. Anything you want to say to me you can say it per email. Have a great holiday"
Try to be direct, short, and sweet, "Please use e-mail for further communication, unless there's an emergency. Thanks!" I'm not sure why you would offer that you feel the children are doing great and there is no need to talk. Note, you said she could use e-mail, but didn't ask her to use e-mail.
