Growing up very fast ie. My daughter at 8 years old already tends to find men attractive and talks VERY seriously about getting married. I mean at 8 years old I was a tomboy only ever interested in boys to fight with em and prove I was tougher!
And no I cannot blame the media alone. My daughter has absolutely no access to porn or any "adults only" materials. She just seems to be developing, naturally, faster than my sisters and I did.

Another point I agree with Miss M is that it was only in like maybe the last eighty years or even less that girls and boys were considered children at the age of 12-16. My own granny married around 14 and she used to tell us that at that time and age this was the norm. I imagine then her mom and grandma might have been even younger when they wed!

Rather than trying to shut down their development, which I believe is a fruitless pursuit, I believe its better then we spend much time and effort in educating our kids about the birds and the bees and of course the beasts. That way regardless of how fast and advanced their sexuality and desires grow, they will hopefully have wisdom and knowledge on their side when choosing to act upon them!