When JRiver get some time to work on Party Mode it should be able to do this, at the moment you can do some limited access blocking... well, not blocking as such - more hiding :)
In summary:
make a smart-playlist to filter out the explicit songs.
In ramble :) -
Once of the things I'm doing with my library is marking songs with explicit lyrics with a keyword 'swearing' (keyword being a semi-colon delimited list you can add many things to it... eg 'swearing;hiccups;incomplete') then make a smart playlist with ' -keywords="swearing" ' [call it what you will to hide it's true purpose, 'My Favourites' might confuse anyone looking at it :) ...hopefully not you too :)] then right-click the DSP-Options button (next the the shuffle button, up there near the progress bar) and select the playlist from the 'Playback Filter'/'Play Only' menu item. Depending on how much the kids (or whoever) knows about MC, they should not even notice. [size=-2](A good party mode feature would be being able to set a filter and stop anyone from change it - 'Lock Playback Filter').[/size]