WA Youth Soccer no longer directly prohibits the wearing of Casts/Splints by players. It now relies of FIFA Law 4 (see below).
SAFETY
A player must not use equipment or wear anything that is dangerous to himself or another player (including any kind of jewelry).
Therefore, whether a player with a Cast or Splint gets to play in any particular match, is totally up to the discretion of the Referee prior to the start of the game in accordance with their interpretation of FIFA Law 4.
In any case, if the Referee determines the player ineligible to play because of a cast or splint - that is the end of the discussion and there should be no further words, requests, pleadings or comments made to or about the Referee on this matter.