I am familiar. My mom and sister were part of it very recently. Sister went to the "training" in Anaheim for two years.
The theology is very similar to the Keswick-Holiness movement. "Let go and let God." Good overview here:
http://andynaselli.com/keswick-theologyExcellent sermon series on the subject:
Major Principles of Christian Living - No Area of Passivity1 of 4
https://www.sermonaudio.com/sermoninfo.asp?SID=10141113295102 of 4
https://www.sermonaudio.com/sermoninfo.asp?SID=10171114362713 of 4
https://www.sermonaudio.com/sermoninfo.asp?SID=1018111431824 of 4
https://www.sermonaudio.com/sermoninfo.asp?SID=1019111256462It started with Watchman Nee and I believe he was influenced by the Plymouth Brethren. After he died, the ministry was led by his successor Witness Lee who turned it very "cultish." They will only read Witness Lee books and filter any question/teaching through his.
As with Keswick theology, the teachings are very mystical and non-concrete. If you don't "get it", then that's because you don't have the Holy Spirit. This is characteristic of the movement as there is a second work of grace in which the Christian moves into a "higher life". (you'll hear a lot about the old v. new man, or carnal v. spiritual man) They rely on key passages such as Gal. 2:20 "It is no longer I who live, but Christ who lives in me." They take this to mean that Christ attempts to live your life for you. Anytime you sin, that's you not "letting" him lead your life (carnal). It can drive a man insane. In one of the sermons above, the pastor describes standing in front of the refrigerator trying to determine if it was him or Christ who wanted a glass of milk before going to bed.
The church itself is strange. There is no organized worship, but rather one "lead by the Spirit." This entails random people talking about the Bible study lesson they were assigned the past week and what they got out of it. Some people stand up and start singing a random hymn in which others join in. All around a tiered circle with elders in front. Also, it's about 90% Chinese.
That being said, it's not a koolaid drinking cult and Witness Lee is dead. Your friend doesn't need to worry about the physical well being of their child. They are just being taught mystical garbage and yes, to be aware of their parents' theology and them trying to lead them away from the "truth" which only they possess.
As the theology is very feminine, I'm assuming your friends' child is a girl. I'm not sure what kind of advice to give. My mom and sister were in it for 3-4 years and it was very frustrating dealing with them. Always wanted to talk about it and when I had questions (because it doesn't make sense), then it was clear I was simply not a Christian or still had a "carnal" mind without the Spirit. Eventually, my mom found something wrong with the church and moved on. She's not in church at all anymore, but her attitude is worlds better. Sister had one more semester of the "training" during this, finished it up and is no longer with the church (or any other as well).