How to use rxjs in react?

Question

React

I need the parent component to follow the function call in the child component.
However, in subscribe in the array, I have a function returned.
How I want my code to behave:
In the parent component, I subscribe to the function of another component.
This function is called on componentDidMount in child component
Here is the link https://codesandbox.io/s/o79139zmzq