Hello,
The best way to help yourkids is to teach them critical thinking skills. Questions are much more effective than accusations. I once asked my then 10 y.o. how he would react if I reached his grandfather's age in this system without Armageddon having arrived. His reply: I'd say "Dad, we got screwed". I knew there was hope for the guy.
Best wishes.
P.S. Emphasize that the decision is theirs to make and you'll support them no matter what. You only want them to have considered all options before making such a life-altering decision. Too many of us based our decision on teachings and doctrines that the organization has since conveniently discarded( the 1914 generation & some annointed must remain on earth at the time of Armageddon ).