oh god, toast. I'm sorry. How bloody mean of her.
Do you think that in future you will want some contact even for the kids' sake, or do you think this is it - that it's better for the kids and you if you simply don't expose them to this disappointment again?
If you think the latter, from what you say, wait for her to contact you. She can't speak to you? Okay, well, wait. And wait and wait. When the call finally comes, be cool. Act cool, even if you don't feel it. Don't ring her back, don't give her much time on the phone. Don't let her speak to the children. Don't bother reading any cards or letters, just bin them. If she gets upset, say "I can hear you're upset, ring back when you're calmer". If you don't contact her, in the end contact will fizzle out.
Either way you'll get a lot of Woe Is Me, and probably quite a few flying monkeys (relatives / friends who try to get involved, often meaning the best). The best thing to say is that you appreciate their concern but it's between your mum and you.
If you think you want some limited contact then again, you can't do any better than just wait and still play it cool. Once you emotionally detach it will be easier. But in this case, ring her when you feel like it. It sounds like she's an emotional sponge soaking up yoru energy and care, so keep calls short, pleasant and neutral. I do think that if you do this, you'll have to warn the children that she can't be relied on though.