Interesting! I have been thinking that genetics are less realistic than they used to be. Maybe it's because I started using mods.
I've had a few cases where children don't look like either parent. My daughter and I laugh at that as another strange sim thing. It never occured to me that the combination of mods and teens could have something to do with it.
I think the most notable I had was a pair of dark-skinned twins born to a very light-skinned vampire with a blue-skinned caster. I suppose the caster might have been a teen at the time. I don't remember. It was interesting though because even though the twins don't look like either parent, they look a lot like each other.