My younger daughter walked away from Christianity when she was in college. She graduated from college and went to Seoul to teach English for four years. I continued to talk to her about Jesus and pray for her. My husband was always telling me to stop talking about Jesus. I spoke to my daughter several times a month.
Periodically, I would get these angry calls and my daughter would ask it I had been praying for her. Yes, I had. Did I pray this and this. Yes, I had. In a snarling voice, she said, well your prayers were answered.
O still laught about it 15 years later. If God can send Christians to my daughter in Seoul, God can reach your child wherever they are. Ask God how to pray for your child. Pray boldly, pray specifically! My daughter returned to Jesus and now married to a Christian husband and they have two children. God is always always faithful.