Two teenaged children (Mia Wasikowska, Josh Hutcherson) conceived by artificial insemination get the notion to seek out their birth father and introduce him into the family life that their two mothers (Annette Bening and Julianne Moore) have built for them. Once the donor (Mark Ruffalo) is found, the household will never be the same, as family ties are defined re-defined, and re-re-defined.