2+2=?

They were four of them. I remember it was one of those see them first days. I just stopped and sat next to the kids. After a minute or two, some grown-ups came and asked for a group taut.
It was some months after, when I showed them their pictures including this one.
They asked me if they can keep it.
BUT YOU SEE, THEY WERE FOUR OF THEM...
AND IT WAS ONLY ONE PHOTO...