This is an urban legend. Information from Perplexity:
The story seems to be a persistent urban legend designed to illustrate themes of selfless love and sacrifice, rather than a documented real-life event.The story you've referenced appears to be a fabricated narrative, not an authentic account.While a similar story is found in a devotional by Dave DeSelm Ministries 1, fact-checking reveals this is not a true story. In fact, the story has been circulating in various forms since at least the 1920s 5. Notably: A 1925 Mary Pickford film called 'Little Annie Rooney' featured a similar storyline
A 1993 'Chicken Soup for the Soul' book also included a comparable tale
The narrative violates medical guidelines, as most countries prohibit children under 18 from donating blood 5