*Walter 6th High Steward of Scotland
born 1293 Dundonald, Kyle, Ayrshire, Scotland
died 9 April 1326 Bathgate Castle, Bathgate, West-Lothian, Scotland

father:
*James 5th High Steward of Scotland
born about 1243 Scotland
died 1309

mother (likely):
*Cecilia of Dunbar
born about <1270> Scotland
died about 1320 Scotland
or
*Egidia de Burgh
born 1263 Ulster, Ireland

siblings:
unknown

spouse (1st marriage):
*Marjorie Bruce Princess of Scotland
born about 1297 Scotland
died 1316
married 2 March 1315

children (from 1st marriage):
*Robert Stuart II King of Scotland
born 2 March 1316 Paisley, Renfrewshire, Scotland
died 19 April 1390 Dundonald Castle, Perthshire, Scotland

spouse (2nd):
*Isabel Graham
born about 1296 Abercorn, West-Lothian, Scotland

children (from 2nd marriage):
*Egidia Stewart born about 1316 died before 1406

biographical and/or anecdotal:

notes or source:
LDS
ancestry.com
"Biographical Encyclopedia of the Kings & Queens of Great Britain" by Mike Ashley
The sources are about evenly split between Cecilia and Egidia as the wife of James Steward.
Ashley (above) states Cecilia as the mother.
The pertinent question is why James & Walter would name their daughters Egidia.