Guns, ICBMS? ;-). Seriously: so far we've kept the kids off by setting a simple password on the front page. As a Swiki is a social environment, if we need to look for solutions I'd look for 'advogato-style' solutions instead of trying to combine 'everyone can enter and edit' with the 'absolutism' of capabilities.
Incidentally, you are talking about policy instead of implementation. This policy could use capabilities in its implementation.
For example, people with the edit-page capability can edit pages at will. People without it must edit in a different way and submit to an editor. Editors have an approve-edit capability.
Something like that, I dunno. The fact that it's distributed over the web makes it more complicated.
Lex