Well, I kind of discuss things very non threateningly. Like, when she says she has never restricted your beliefs, say thank you and all you are asking is that she extend the same courtesy to your children. When she says you have no idea what it's like, then say, she's right, but she fell in love with you as a non-JW, so that must mean something worthwhile came out of your belief. You just want your children to have the opportunity to form their own beliefs, and it if really is "the truth" then their being exposed to other religions will not be a deterent to their seeing "the truth". Also, point out that if you aren't allowed to share your thoughts and ideas with your children, it could damage your relationship with them.
If all else fails, try to gently point out that you are the "head of the household" and that your decision is that your children will participate in things with you as well as things with their mother. If she cries, hold her and comfort her and say you both want the best for your children, and that's what's most important.
Again, I haven't experienced this myself, so I hope my advice doesn't sound too simplistic. I hope things work out for you and your family.
Happyout