Two or more touchs at same time?

Hey Guys, in my scene i have an empty game object that is holding another 3 objects (childs), this objects contain each one a circle collider. I did an prefab of this, and will be "spawning" this object very often.

But, every child need to recognize when it's been touched (tapped) and realize some action (execute an function inside the script), i was thinking of 4 objects touched at once, maybe more, and the child do not need to be from the same prefab. If you touch 1 or 4 (or more) objects, they need to recognize that are been touched and execute the action.

How can i achieve this? I mean, the OnMouseDown function is not Multi Touch so i guess i will be needing to use the Input.Touch option.

Can someone give me the idea of what i need to achiev? I need to store the fingerId or maybe the touch in an Array/List, use raycast, make this script for every child, maybe an general script that will handle all the touches in the game or something else?

I'm not here asking for a prompt solution or any code, but for someone who has some experience could enlighten me in this situation. I'm completely lost , apparently handle multitouch is not so trivial.