Oh come on NOW. The average 12 year old is pretty clued up. I'm sorry, but I have an 11 year old neighbour who knows what blowjobs are and everything! And most kids that come online do their fair share of 'investigating'.
By making the forum for all age groups you're unfortunately undermining the larger majority of the users. Most users of the harbor are MI fans, and most MI fans are fans of the old games and are about 16-25 (Am I right?).
By employing silly, baby rules you're certainly making it safe for younger children, but alienating your older and more faithful forum users, hence turning them away.
I think the rules should be reconsidered slightly and younger users are the ones that should be undermined, not the older ones.
You might recognise me.