I agree with OTWO, my children were brought up as Witnesses, both saw through the religion long before I did.
Neither feel they were harmed by being in the religion until their teens.
You have nothing to fear from the contact with Witnesses old or young, if you do as OTWO says, and explain everything, no matter what age your children are, don't hold anything back.
They can understand the whole picture, their brains are hardwired to take on new concepts, such as cults and mind-control etc.
I know when I was a kid , my Mum would half explain something, thinking I should be protected from all the info. and I had to struggle to fill in the gaps, like the time I asked at about four years old "What is rape?"
Do as Shelby says, be more loving than the Dubs, explain it all to your dear children, and strength to you !