Prancer

Prancer is one of the Aelur, a man of Free Sky. His wife Heartbud is the sister of Nightsinger. They have four children, first mentioned in The Tenth Lady:

Robin - four-year-old daughter

Thrush - four-year-old son

Finch and Sparrow - two-year-old son and daughter (which is which isn't clear)

The four may be two pairs of fraternal twins, or simply born closely together.