Alpha masking multiple 2D Sprite GameObjects with 1 Sprite GameObject

After days searching and not coming up with anything useful I decided to ask my question here. I hope you guys can help me out!

What I'm trying to do is have a GameObject which has a sprite with fully alpha transparent parts. I want all children of this GameObject to be masked by the parent "mask" sprite.

Basically the hierarchy would look like this:

I want to be able to animate the child sprites. So I could do something like this:

So the "MaskGameObject" has a sprite with a filled circle, outside the circle it's fully transparent. The moving stars are multiple child gameobjects of the sprite.

I will be using several of these MaskGameObjects at a time in a scene.

I read about using multiple camera setups, this seems a bit overkill. Performance is important, I'm making a game for phones.

Please help!

Regards,

Pascal