Well it's said to be the smallpox vaccine
Often confused with the tuberculosis One
Some Anon said once It was a way to collect everyone's DNA...

Doesnt seem too far fetched...

I think it's the DNA taken at birth. I have it too, and from a young age, as children we found out and played the game of who was human and who was not. Humans have had this, robot not, just for clarification. Later in adulthood I thought about this many times. By the way, this game was taught to us by my friend's grandmother who was a renowned herbalist in the area.
Later on, they supposedly started taking DNA samples from the heels of babies born fresh and sending it to the central bank in the Vatican along with the original birth certificates (i.e., a promissory note stating that your parents put you into slavery through tricked corporate fraud/fake states). I don't know how much truth there is in that, whether the place was really the Vatican's underground archives. But they say that there's a grain of truth in every rumor.

Do today's young children also have this, or not?

"Do today's young children also have this, or not?"
Good question... Does anyone know?

There's one other thing that's been on my mind. The shape of the scar. We all have the same one. Except that an injection wouldn't scar like after a missing piece of skin. That's why I think it's a DNA sample. The blood dries, gradually crumbles and "disappears". But a piece of skin remains and with it the DNA sample.