Q: #63. (Question from a 10 yr old!) If demons, who are fallen angels can live inside of a non-Christian's body, can good angels live inside of a Christian's body?
A: What an amazingly deep question, ESPECIALLY from a 10 yr old! I have to admit, I have never once considered it. Honestly, I am not sure that the Bible directly answers this question, but let me tell you how I would answer.
First, you are indeed correct that demons (fallen angels) can live inside of those who are not Christian. There are also some Christians today that believe they can live inside of a Christian. This is false, dangerous, and totally un-Biblical though. (See my study: Can a Christian be demon possessed?)
When a person becomes born again, the most amazing thing that occurs is that God actually comes to live inside of that person in the form of the Holy Spirit (Eph 1:13-14)(Eph 4:30)(2 Cor 5:5)(2 Cor 1:22). This is why I would say good angels do not live inside of a Christian. Because God lives inside of a Christian, good angels would not live inside as well. This is also why demons cannot live inside of a Christian. God and demons cannot live in the same place (Mk 3:25)(Lk 11:17)(1 Pet 2:9)(Acts 26:18).
In theory, I suppose your (brilliant) idea would be correct, that good angels COULD live inside of a Christian just as bad angels can live inside of a non-Christian. However, because God lives in the Christian, good angels do not need to, and bad angels cannot.