Of all the things you can do with your friend in a game I’m sure you’ve never got him/her pregnant (we’re not talking about real life here people) but now thanks to the naughty minds at Lionhead Studio you will be able to. Here’s the lowdown taken from an OXM article:
The team seems committed to ensuring the [co-op] experience is in no way compromised. You’ll be able to enjoy, ahem, intimate moments with your co-op friend and eventually produce offspring together.
I can't wait to knock up one of my buddies.