Ugottabe, as parents we must remember that we have helped to indoctrinate our children into this weird jw belief system...and that they wouldn't be there had we not placed them in it (for the most part).
So of course when we tell them that we no longer believe, the spiritual foundation of their young lives just comes crumbling down, or at the very least forms a large crack. I would guess it could have the same effect as telling them mommy and daddy are getting divorced. I remember hearing that my worldly parents might get divorced and it was crushing, not because we had a happy family (unless you like waking up in the middle of the night hearing them fighting) but it was the sense that everything we trusted in could suddenly vanish. A lot has to do with the age of the children, I'm sure. Once I was older, I could see that everyone's life would have been much better had the divorce taken place. Sadly, my parents stuck it out to keep us kids happy...and they were miserable.
Anyway, the best course is to be calmly honest as you've been (applause!) and tons and tons of unconditional love. I used to ask, "how would Jesus have treated that person or handled that situation?" It shows how totally off-course the org is without throwing stones, and it helps kids/others to think rationally.
You've given your kids the best shot at a healthy life! So proud of you. Now you'll need to lovingly pave the way for them to follow you out. (((hugs))) You'll get lots of support here on this wonderful forum.