I was able to get both of my kids out, despite my husband being all in and continuing to take them to meetings and trying to indoctrinate them. It took two years and constant effort, as in every single day.
What worked for me was to find out what "their" issues or pet peeves were and then validate those feelings over and over. Trying to prove evolution or things like that was just over their heads and didn't matter to them, so that approach didn't work.
With my daughter, she thought that the meetings were boring, so even though she had to go with her dad, I validated her feelings. If she came home, I'd ask what the most boring part was and how many times she fell asleep. If they didn't go for some reason, we'd do a little victory dance and then go do something fun instead. She gradually would look for reasons not to go. She's also very social and wanted to keep her friends at school despite being told constantly that they were bad association. So I tried to find ways for her to do fun things with her friends and then we'd talk about whether her JW friends were really "better" than her school friends. I also pointed out what happened to my JW friends when I stopped going to meetings (never heard from them again) and how her school friends would never do that kind of thing just because she had different beliefs. Validating her in these ways led her to be able to trust her other feelings about what she was being taught and she came to her own decision at age 11 that she never wanted to be a JW.
My son had different issues- he really wanted to celebrate holidays and birthdays and didn't understand or "buy" the JW explanation. Of course, we couldn't openly celebrate anything because his dad wouldn't allow it in the home, but I would talk to him about what it would be like if we could, I.e. What would he want to do for his birthday party and who would he invite? How would we decorate our first Christmas tree? What would he dress up as for Halloween? We joked about which one of his friends we'd have to behead at his birthday party because that's what the bible says happens. It took much longer with him- about two years- before he finally opened up and said that he had never wanted to be a JW and that he wanted me to help him find a way out.
Unfortunately, the only way out was for my husband and I to separate, which has been difficult for all of us, but the kids are now able to focus on making their dreams a reality and we're going to have really wonderful year of "firsts," including my son's first birthday party at which he recently had a blast with his friends.
So, I guess I'm recommending meeting them on their level, letting them go at their own pace and constantly validating their feelings so that they know they can come to you without judgment. It was worth the long battle!