The American television series Little House on the Prairie, first broadcast 1974-83, was a remarkable nexus tying together a number of people in this list of famous adoptees. The author of the books on which the series was based, Laura Ingalls Wilder, was a [probably unofficial] adoptive parent of two men: Roger Lea MacBride (who also edited and wrote later books in the series) and Rexh Meta. MacBride himself was also an adoptive parent.

Of the actors in the series, at least four are definitely or possibly adoptees: Melissa Gilbert, her brother Jonathan, and the brothers Patrick and Matthew Laborteaux. This is in addition to at least two story lines in the series which involve adoption.

References

Trenta, Alex, et al. "Trek to the Stars: Little House Nitpickers Guild: General Nitpicks." Available at: http://www.geocities.com/TelevisionCity/5812/lh-nitgeneral.htm
"Little House on The Prairie." Available at: http://www.geocities.com/TelevisionCity/9348/little_house.htm