But if you live in a community where your only options are live immature churches or dead doctrinally sound churches. I'd go for the live churches every time.
The reason for this is that God cares more for how we love him than what we know. He would rather have a church do what they know, than know but not do. We are saved by Grace whether we can articulate what that means or not. Many, who know their doctrine inside out will not be there when the role is called, but many who have no idea what they believe, they only know Jesus, will be there.
So are you in sin? I don't know. Were you in sin to believe immature things? I don't think so, you were just immature. Was your little girl wrong to draw crazy pictures and call them pictures of you? I don't think so. I think she was doing the best she could with the skills God had given her. I think that's probably true of you too. We don't measure godliness by what we know. We measure it by who we know and how we know him. I would say that if you raised your children in the Lord and they are raising their children in the Lord, you've probably done a good job and God has been blessed by your life so far.
Do I think you should rest on your laurels and just sit content? I don't think so. I encourage you to continue to grow and mature in Christ. Don't forget that it is knowing God that is important, not knowing a lot about him. But study, pray, dandle your grand children on your knees, do a lot of hugging. If you are content where you worship, stay. If there is somewhere you think would help you mature in a healthy way, move on. If you decide to move, do it with great graciousness without pointing out everyone else's problems. Be kind and sweet and be very careful not to burn any bridges or to do anything that might allow anyone to disparage God or the Reformed version of the faith.
Never forget that those folks in the immature church know the same God you know. And they will be sitting right next to you in glory one day, throwing down their crowns just like you. They will go a bit further in their becoming like Christ when they see him as he is, but since we'll all be moving a long long way, it might not be all that different.
I hope this helps.