In Welsh mythology, the pantheon is generally agreed to be divided into two warring camps: the Children of Don and the Children of Llyr. The Children of Don are the decendents of the goddess Don and god Beli (also called Beli Mawr, Belin, and Belinos/Belinus), and are more or less analoguous to the Tuatha de Dananns of Irish mythology. They were often at war with the Children of Llyr for the kingship of Prydein (Britain), and according to the Mabinogion won.
It may be that they are later gods of the Celts, as opposed to the family of Llyr, who may have been indiginous gods; the family of Don seem to represent civilization (agriculture, smithing), while the Children of Llyr are more primal, dealing with natural forces (the sea; death; love).
The Children of Don (or Family of Don) are as follows:
These are the actual children of Don and Beli:
Gilfaethwy: lovestruck brother of Gwydion and Arianrhod who rapes Gowein in The Mabiongion with Gwydion's help.
Afallach: "Apples" king of the isle Afallach/Avalon in some myths; father of Modron in some Welsh genealogies.
Caswallawn: usurper of Manawyddan ap Llyr and killer of Caradawg ap Bran; king of Britain. Possibly confused with the historical Cassivelaunus.
Llefelys: "Speaker"? (some possible relation to speaking) made into legendary king of Brittany.
Nudd/Lludd: Lludd: "Obstacle" Nudd: "Fog" god of war; related to Irish god Nuada. Later made into legendary King Lud of Ludgate and supposed eponym of London (Caer Lud: Lundein). He is sometimes confused with Llyr
Amaethon: "Plow" god of agriculture.
Gofannon: "Smith" god of smithing.
Peibaw: made into legendary king. Turned into ox with his brother Nynniaw after a fight over who was stronger; these oxen pulled the chariot of the sun. This may be a later invention, though.
Nynniaw: made into legendary king.
Penardun: "Sovereignty" wife of Llyr in some texts; goddess of the land, like the Irish Eriu.