Interracial families: When genetics only go either way...

I think some of it is down to TS4 not blending facial features too and more-or-less taking them as-is from either parent as well. People in real life can and do grab both their coloring and features from one parent (Rashida Jones comes to mind) but it's nowhere near as common as it is in TS4. Like with how two of OP's kids got not only their dad's light skin and blonde hair but also his small nose or thin lips with zero change.