Why are 12 year olds having sex???!!

Jessica • 21 and in a very happy relationship (:
Is anyone else weirded out by this?! I'm super conflicted between helping these children figure themselves out, and telling them to stop?! I lost my virginity at 15, which I agree is young, but I'm seeing girls on here saying their 13 or 12 asking about the 4 guys they've already slept with!