That is a very hard situation.
I have heard that the most important thing to do is to let you know that you will love, support, and accept them as your children even if they are not frum or anything.
And that should really be the truth also. We don’t know what a person’s ??????? are. You are their mother, and know them better than anyone else, but I am sure there is much that you don’t know.
The passuk in malachi says about the the yemos hamashiach: ?????, ??????, ??? ????, ????–??? ???? ??????, ???? ?? ????.
We will only be able to tell the difference then, we can’t tell now.
You know how much your kids have been through. If there is one thing that will make them come back and love Hashem, won’t it be your unconditional support?