I don't have kids that attend the meetings, but I do have kids and JW relatives who have tried to get them to the meetings and/or do informal witnessing.
I "innoculate" my kids by showing them independent thinking on JW and non-JW topics. And, my mantra is that life isn't black and white and there is always multiple, multiple sides of every story!
I've tried to learn the more mainstream viewpoints on the Bible. For example, the Memorial. My relative made a big deal about the Memorial, and said that they were the only religion that followed Jesus command to remember him. . . to my kid! I quickly reminded my kid that when we went to a Catholic church with a friend, there was taking of the bread and wine, and that Catholics (and many other religions) do this on a more frequent basis. And, I quickly reminded the relative that Jesus didn't give a time table on when to do the remembering and to go check the scripture. Of course, the JW is a "JW for feeling" and barely knows the JW spin and could not even come close to defeating me in my argument.
After that, I had a conversation with my kid in that no one is allowed to talk about the Bible/God/religion with them without me present. And, I told my JW relatives of this fact. No problem since. But, I stll keep moving on.
I also try to explain the perils of idealism (and closedmindedness which quickly follow). Idealism is throughout our culture and the pressure the group a puts on individuals to conform is unrealistic. Plus, idealistic people are often trapped in cults.
As the child approaches middle school, the teaching of past cultures comes into play. There, you can teachthe child that the past culture's gods, were just as much (if not more) revered by those ancient cultures as ours. Now, all those gods look silly, but today's people will defend their god to the hilt. In other words, I am trying to show my kids the fallacy of "My God is better than your god" thinking. And, there is higher capacity for scientific views . . .