Are the parents ones you created or are they townies? For the most part, townies can be generic, more in the middle of the slider with just a few changes.
For created sims, such as what I use, the kids do seem to take after their parents, until I have them marry, then the looks of the other sims get mixed in. In one family, the girl that my sim married has a big hump in her nose. Real obvious, and unfortunately, it showed up for two or maybe three generations before it was finally replaced. In a townie family, the male sim has a horrible mouth and that passed down for three generations.
If you want to make sure that there is a wider range in the looks of your sims, you can use the cheat and go into CAS and change their looks.
I don't know if this would be of any help, but if you want to check out how genetics can change or not change, go to completed project stories, I just completed my Random Town Jump, took a couple and moved the heir to the next town to marry someone there and move that heir to the next town t marry and continue to cover seven towns.
At the end of my completed story I have the seven generations from the founder family, townies, to the last family and showing what their offspring would look like at YA. Lombardi family. You don't have to read the story, just check out the photos at the end of the story. I didn't do any changes to the looks, as it would affect the goal of the game, to see how genetics affected over the seven towns.
hope this helps you
