What about communicate between presenters?

I need show progressbar in parent fragment in case if child fragment has needed state (for example count elements in `ListView`).
To solve the problem it is necessary that the presenters were able to communicate. The `MainPresenter` should know about entities size in the `ChildPresenter`. Is it correct from the point of view MVP if the presenter will know about another presenter? And how this approach can be implemented in Clean Architecture?

``` java
====== Main =======

public interface MainView {
void showLoading();
}

public class MainFragment implements MainView {

ChildFragment childFragment;

private void init(){
childFragment = new ChildFragment();
view.add(childFragment);
}

public void showLoading(){
// show progressbar
}

}

public class MainPesenter {
public void showLoading() {
getView().showLoading(); //show only if ChildPresenter has count > 0
}
}

====== Child =======

public interface ChildView {
void showList(List entities);
}

public class ChildFragment implements ChildView {

public void showList(List entities) {
//show list on UI
}

}

public class ChildPresenter {

List entities;

public void init() {
entities = getEntities();
getView().showList(entities);
}

public int getCount(){
return entities.size();
}

}

```