I was watching Coronation Street the other night with my ten year old daughter. It showed someones door with the word 'SLAG' on it and my daughter asked what that meant. Caught a little off gaurd I said it just means a not very nice person usually a women bit like a tramp, and that it is a very hurtful name to call someone. Did I do the right thing? I did look it up in the dictionary but just gave a definition of a slag heap.
I always start with the line - what do you think it means? that way you can get an idea as to what their level of understanding is and how to address the question in such a way that is appropriate.
I would think that it is not appropriate to allow a 10 year old watch a programme like Coronation street. The situation you were faced with was trying to explain 'Slag'. Next time, you may be forced to explain an act. I think the exposure is a bit too early.