I focused on teaching my daughter about controlling organizations from the time she was 6 ( when my husband began his re interest in the JW) I wouldn't mention JW specifically, but focus on the tactics of controlling organizations and how dangerous they are. I then used multiple types, MLM, some political groups, and also religions.
Eventually I would casually mention a thing or two about the JW. Then explaining that I worry about what would happen if her Dad became baptized. When she was a preteen I mentioned more difficult things like shunning as a fear, then quickly say there is no way of knowing if her Granny etc would actually do that, but the Watchtower teaches them they must, and they would get in trouble if they disobeyed that instruction. I would mention things like did she notice her granny never mentioned Christmas etc, and then explained why. This was over a period of many years that I would bring it up. Eventually she put the pieces together and asked if the JW were a cult. I answered that many people believe that they are. Books have been written on that.
I would not have a long conversations with her, but short ones so she didn't feel lectured to.
It worked for my daughter. At this point I believe she is inoculated. Thankfully, since she is now just turned 15, and living with her Dad since September. I insisted he move out due to physical abuse and constant verbal abuse, and he convinced her she needed to be with him, or should I say guilted her. He also has been " sharing" about his feelings, and telling her I am mentally unstable. The usual words of an abuser trying to change the perception of reality.
But that is another long story.....