So, I was showing my daughter how to drop one person onto another to make a baby and got confused over which one was the dad. They had a son already who was 18 I think and I dropped him onto the Mom and they went off and tried to make a baby (thank goodness nothing came of it) So, is this a glitch or can there be inbred babies?

As stated by LadyCFII in this thread that situation is a bug and will be fixed in the next update.

Thank you! I had a hard time explaining to my daughter what was going on there. It was a bit unsettling!