Prior to Little House on the Prairie debuting on September 11, 1974, they starred in the made-for-television drama Sunshine (1973), as Jill Hayden.
In the final season of the show, the absence of the family members (except Laura) was explained by their relocation to Burr Oak, Iowa, in search of a better life.
The twins starred in commercials for, among others, Doublemint gum, Mattel Toys, and Kentucky Fried Chicken.
Sidney was married to horse breeder William "Rocky" Foster for nine years, until his death at age 55 in 2009.
They originally met on the Little House set at Big Sky Ranch in Simi Valley (where exterior scenes were filmed) when she was a small child and he was a teenager who lived nearby.