I think what your looking to do is this :
You grab a reference of the child actor > Get child Actor > Then cast to the child actor, as shown above. As you can see i was able to get that “NUM” int you were talking about and also Call it’s function to set the int. You could also use “Interface’s” Well I hope this helps. 
Here’s what i said above:
子アクターの参照を取得します>子アクターを取得>次に、上記のように子アクターにキャストします。ご覧のとおり、私はあなたが話していた “NUM” intを取得することができましたし、intを設定する関数を呼び出すこともできます。あなたはまた "Interface"を使うこともできます。
I hope what i said is well translated, as i dont speak Japanese, so if it said something inappropriate blame google がんばろう