How can I remotely read Wechat messages on my kid's Android mobile phone?
You will need to use the service of an application that was designed for this type of procedure. I searched Google and found out FlexiSpy. It's a remote monitoring application that gives parents the possibility to see what they kids do with their phone and who they talk with.
You can read more about it using the following information: http://www.flexispy.com/en/mobile-child-safety.htm
