It is a good topic, because you can argue that every single Prince of Wales who died early radically changed the course of British history by his death.
1) Edward, the Black Prince: [age 46] married with children
2) Edward of Westminster (son of Henry VI , first husband of Anne Neville): [age 17] married no children
3) Edward of Middleham (son of Richard III and Anne Neville): [age 11] never married
4) Arthur, Prince of Wales (older brother of Henry 8th): [age 15] married no children
5) Henry Frederick Stuart, older brother of Charles I: [age 18]never married
6) Frederick Louis, father of George III: [age 44] married with children
7) James, the Pretender to the throne (son of James II and Mary of Modena):[deposed] married with children
@ Prince Albert Victor, Duke of Clarence (Prince Eddy) was 2nd in line to the throne, but died before becoming the Prince of Wales.
1) Edward the Black Prince death left his ten year old son, Richard II as heir. Richard II was highly manipulated as a child king, and was later deposed. Every historian believes that his father would have been a strong king, and perhaps his son would have done better had he succeeded as an adult.
2) Edward of Westminster was killed at the Battle of Tedwsbury, and as a result was the only Prince of Wales to die in battle. Technically he ceased to be Prince of Wales three weeks before his death when his father was deposed. It is a matter of interpretation, but he is usually considered one of the Prince of Wales who died before becoming king. His widow married his enemy (and murderer according to Shakespeare). She then gave birth to another Prince of Wales who died before becoming king.
3) Edward of Middleham died exactly 500 days before his father, and 340 days before his mother. Had he lived he would have provided a credible alternative to Henry Tudor as king. We may never have had the Tudor dynasty.
4) Arthur Tudor is famous. Did he or did he not have sex with his wife? One of the most debated wedding nights in all of history.
5) Henry Stuart was not married when he died of typhoid fever at the age of 18. He was extremely popular, while his father was fairly unpopular. Had he lived there is a good chance the civil war would never have happened and English history would have been radically different. Most historians agree that the personality of Charles I was a significant reason cause of the civil war.
6) Frederick was a very popular man in Britain. His early death at age 34 left his son a victim of his father's abuse. Speculation is high that the ill feelings generated by the handling of the war in 1763 by George III, would have been handled very differently by Frederick. George III handled the war badly, and tried to tax the American people to pay for the cost of the war. The taxes and the way the colonists were treated were the primary reason for the war. It is possible that the loyalists would have held sway had Frederick lived and the American Revolution wouldn't have happened.
7) James was declared the Prince of Wales in France when he was 24 days old. So he is th 7th POW who did not become king, but his title was officially revoked. Of course he and his son, Bonnie Prince Charlie, mounted a credible campaign to take over the monarchy.