Like Andy said, age of consent doesn't mean people stick to it. Not many teenage girls are going to shop their boyfriend to the police because they are underage, are they? Unless they are feeling REALLY mad that their first time wasn't all that...
I haven't counselled anyone younger than about 14 - but the lady I work with has had 12 year olds come up to her thinking they are pregnant. It happens a lot and part of it is down to the fact that kids really do gorw up very quickly these days - puberty kicks in a lot earlier than it used to and children as young as 8 are starting their periods, so it's not uncommon to find pre-teens being sexually active. Scary, but not a rare thing.
Mix a little alcohol with an older boyfriend and there you go...