Sexual behaviors in kids

Do kids and pre-teens naturally have urge for sex or it was learnt from what they see?
Halle Berry, an iconic Hollywood actress has revealed she experienced her first orgasm when she was 11 years old.

She made this revelation as she recalled the first time she explored her sexuality.
Recalling her first experience of self-pleasure, she said: "I remember my first orgasm… I did it to myself."
She continued: "I was diddling. I was figuring out my sexuality, like most girls."

There are other scenarios where kids are seen fondling each other or actually getting down in the main act. 

What's your thought about kids and pre-teens sex. Is it natural, or just curiosity?