To be more careful about the titles they list in the Mumsnet Talk 'Discussions of the day' box to the right of the threads?
For example today there is listed a (partial) title which reads Woman simulates sex with headless baby... 
I've seen other inappropriate titles in the past, which you might not want your dc to see. You can avoid clicking on threads with dubious titles, but you can't do anything about this. Surely there could be some judicious editing?