Send an event to each, to change it's properties? Or loop through all of them on an event and change the data to whatever you want. You can also send event with data.
So, you would find the main gameobject first,(Find GameObject) then find and count all of it's children objects. You can loop through them with Get Next Child action and count with Get Child Count. - You would do all of this on a global event, so all these actions would only fire on that event. And you would send that event from whenever you want that action to fire up
On the loop child state, you would get the component that you need (Get Component action), and set property of that component on each child, then finish that state, and loop it back to the loop state, once the loop goes through all childs it will go to finish state.
Also, a quick tip: just in case if you want to find a disabled gameobject, you can do so by finding it's parent first, and then finding it as a child of that parent. Otherwise if you find by gameobject, it won't work with disabled objects.