When I was DF'd and made a decision not to return my son was only 4. My parents still did their part to indoctrinate him and he insisted on going to meetings with them quite often (I know - if I knew then what I know now I would have stopped that - but that's water under the bridge)
I spent many hours explaining to him why I did not believe it any longer, and having to suffer through him being upset with me for not going to meetings. I just kept giving him information, explaining things to him - as much as I could in a non defensive way.
By the time he was 13-14 years old he barely went to meetings - mainly only when his grandparents guilted him into it. But he still defended them and their shunning and he still thought they were the "truth" Still - I tried my best not to put him in the middle between me and my parents and to just give him information. And I did my best to keep him involved in other positive things, like sports, school activities, etc. As time passed, he got more involved in sports and his friends, and eventually he quit going to meetings all together.
He's now 20 and at college. I was visiting him this weekend and during one of our conversations he told me how glad he was that I had left the JWs when I did. He said he realized now how messed up his life would have been and he was glad that I stood my ground and didn't let him get mixed up in that.
It was a lot of years of frustration and hard work (and tears) - but man am I glad I hung in there! Just wanted to pass that little tid-bit along to all of those out there now going through what I did. Hang in there - keep giving them information, without putting them on the defensive. It's hard - but it does pay off! Don't give up.