Why add_child funtion not work when i used it in _ready functon?

[bge2]

thanks ,i get error like this.

Parent node is busy setting up children, add_node() failed

Attention Topic was automatically imported from the old Question2Answer platform. Asked By Huder I have an error that i completely not understand, what is this? I tried solution that this error said but call_deferred() not exist anywhere, documentation can’t search it 0:00:00:0541 - Parent node is busy setting up children, add_node() failed. Consider using call_deferred("add_child", child) instead. ---------- Type:Error Description: Par…

thanks i understand about t.

E 0:00:00:0892   test.gd:12 @ test(): Parent node is busy setting up children, `add_child()` failed. Consider using `add_child.call_deferred(child)` instead.
  <C++ Error>    Condition "data.blocked > 0" is true.
  <C++ Source>   scene/main/node.cpp:1420 @ add_child()
  <Stack Trace>  test.gd:12 @ test()
                 test.gd:5 @ _ready()