I add my heartfelt sympathy and agree with all the advice you've been given so far, but I will add, as a warning:
Keep him away from your parents and other JWs! Especially and absolutely in regards to time alone with them! If you are not there, they will be working on him constantly.It is worth whatever you have to do to replace the babysitting aspect of the relationship.
I know this from experience. At one point my mom had my sister's kids, and would not let them get on the plane to go home, told them their parents were probably getting a divorce, (untrue) and only wanted them there longer to work on them more. Be vewy, vewy cahful Wabbit!
Also, keep reading the Bible with him, so he will not only associate it with the witnesses. Make sure you have a translation other than the bogus NWT.(There is plenty of info on what they did to it around, it you are still not convinced of it's error.) He needs to understand the freedom in it, before he grows up and rejects it all cause of the Witnesses.(For that matter, there are lots of little bible classes in different churches that have programs with stickers and patches, some like the boy scouts and eagles,like the Royal Rangers...if you ever want to look into it, I can tell you about a few--I am non-denominational by the way.Just PM me)
Lord bless you and help you heal. Whatever you were DFed for, it does not estrange you from God, only JWs! Count it a blessing in disguise!