Ummmm... Ill try to answer... not expert though..
There are alot of kids on BYC.... so not anything you wouldn't say to your best friends 8 year old. Who knows what kids will click on.. and it's nice they get to learn about a fun hobby themselves here! Without learning what their parents wouldn't want them to, that is.
And by 'clean up' ... it just means they ought to go back and edit out things they have said that would be inappropriate.
An innuendo, is something said alluding to an inappropriate topic without coming right out and saying it. A read between the lines type thing.