https://kids.guinnessworldrecords.com en

Youngest player to play in a Major League Baseball (MLB) game

Youngest player to play in a Major League Baseball (MLB) game
Who
Joseph Henry Nuxhall
What
15/316 year(s):day(s)
Where
United Kingdom
When
10 June 1944

Joe Nuxhall (b. 30 July 1928) pitched for the Cincinnati Reds against the St Louis Cardinals aged 15 years 316 days at Crosley Field in Cincinnati, Ohio, USA. The game took place on 10 June 1944, four days after the D-Day invasion in Europe, with all Major League baseball teams affected by the draft. Nuxhall did not play again in the National League until 1952.