Offsetting the answer into the world of pigs is a really useful mechanism, in that it softens the nature of what you're about to say, which can be alarming to an 8 year old. After all, nothing like his stuff happens in the Lego movie.
'Well, you know when Daddy wants Rosie to have piglets, he puts her in with Kevin, doesn't he?' I began.
'For the mating?' asked Sam. 'What happens in the mating?' As a farm-kid he's already au-fait with some of the terms even if he doesn't fully understand the technicalities.