William and his wife Matilda of Flanders had at least nine children. The birth order of the boys is clear, but no source gives the relative order of birth of the daughters.
Robert was born between 1051 and 1054, died 10 February 1134. Duke of Normandy, married Sybil of Conversano, daughter of Geoffrey of Conversano.
Richard was born before 1056, died around 1075.
William was born between 1056 and 1060, died 2 August 1100. King of England, killed in the New Forest.
Henry was born in late 1068, died 1 December 1135. King of England, married Edith of Scotland, daughter of Malcolm III of Scotland. His second wife was Adeliza of Louvain.
Adeliza (or Adelida, Adelaide) died before 1113, reportedly betrothed to Harold II of England, probably a nun of Saint Léger at Préaux.
Cecilia (or Cecily) was born before 1066, died 1127, Abbess of Holy Trinity, Caen.
Matilda was born around 1061, died perhaps about 1086. Mentioned in Domesday Book as a daughter of William.
Constance died 1090, married Alan IV Fergent, Duke of Brittany.
Adela died 1137, married Stephen, Count of Blois.
(Possibly) Agatha, the betrothed of Alfonso VI of León and Castile.[w]
There is no evidence of any illegitimate children born to William.