How old are your children?
I think you need to tell your children ahead of time that you want to speak to them. Then arrange an evening, after dinner. (setting them up like this lets them know that this is serious and prepares them for something big - because this is big).
Then in between make a list of what happened between your mother and you, methodically. It's likely to be rather emotional to do it, but just keep persisting.
At the meeting tell them that relatives are trying to get in touch with them because their grandmother wants to see them. Then explain what went on both with the things that happened and most of all the dynamics of playing golden child and scapegoat.
If you can, also point to incidents where they might have seen something a bit odd, something that didn't add up even if it wasn't quite obvious. Let them begin to see what has gone on.
Then point out that her story will be different. Refer to times when they have had an unpleasant incident at school but other people have disbelieved it or not seen what's going on. Your situation with your mother is like that.
Give them time to take this in. Let them ask questions, even skeptical ones. They may have a lot to take in and it may take them time, but you'll be starting the process of questioning off.
I would recommend letting them make their own decision about contact. You could say that you're not happy about them having contact but that it is their decision and in their hands.
Taking it pretty seriously letes them know that what happened to you is NOT ok.
Also, consider therapy for yourself. it's not the answer for everyone but it can be very helpful.
Good luck.