This is a really tough question and situation.
Based on your post I assume you don't want your kids to choose being dubs unless they've heard the pros and cons of being one.
What you say and how you say it really depends on your relationship with your wife and other dub family members. Kids aren't real good at keeping secrets. So whatever you tell them will get around. If you don't mind getting disfellowshipped or having your wife really angry with you and quite possibly being labeled an apostate there are many things you can do.
Do you currently plan on remaining a christian? If so, you could find some literature (both hard copy and online) aimed at christian parents and children. For the younger one an example would be WhitsEnd.org. For yourself family.org may be helpful as well.
Whether remaining a christian or not I recommend teaching your children to think for themselves. Teach them critical thinking abilities. I use television commercials aimed at children as a prime way to accomplish this. If you want more detail on that feel free to pm me. Your witness wife shouldn't object as long as you don't use the WTS in a direct reference.
I also make sure my children understand that anyone who says they have all the answers DOESN'T.
Good luck.