Grazed Knees

I saw a child fall over head first onto the tarmac today.

He was wailing and crying even as his father picked him up and carried him off. There was no blood, but the way the kid was crying you would have thought someone cut his arm off.

I remember crying like that when I was that age. It just got me wondering about the threshold for breaking out into tears about that sort of thing. At what age do you just grit your teeth and pick yourself up?