How to pass click event to sibling underneath in Qt?

I have two overlapping widgets in a window child A and child B. Child A is above B and gets mouse events but sometimes the click should pass through and eventually hit child B.

The ideal solution would have been to use event->ignore() but this passes the event to the parent widget, not siblings.

The "pass all" solution setAttribute(Qt::WA_TransparentForMouseEvents); does not work either because child A needs to capture some events.

How do I tell Qt "I do not want to handle this event, act like I am not there" ?