At one point in the story, I decided to write a chapter about Samuel, simply because I didn't know what would happen next to the Raingolds. To do this, though, Samuel needed siblings. I have a little notebook full of fictional families I've made up, and so I looked through that to find a Samuel that would suit the part. I couldn't find very many Samuels, but I did find one family that had one with several older siblings, a twin sister, and a younger brother and sister who were twins. These were the Polks. I decided to use this family with a few alterations. For one thing, I never mention whether or not there are any older siblings. For another, I changed the ages of the girls so there were no twins. Then I had the Polks as can be known from The Experiment: Samuel, Samantha, Timmy, and Tabby.
Their part in the story expanded slightly from the tiny chapter I wrote while stalling the Raingold part. Their chapter doubled in length, and Tabby had a role to play at Courtstone. Their main role, however, is to show that these events are happening to others, and to expand the Raingolds' acquaintance. And that role they fulfill very well.