The words innocence, innocents sound the same but have different meanings and spellings. Why do innocence, innocents sound the same even though they are completely different words?
The answer is simple: innocence, innocents are homophones of the English language.
The state, quality, or virtue of being innocent, as:
Freedom from sin, moral wrong, or guilt through lack of knowledge of evil.
Guiltlessness of a specific legal crime or offense.
Freedom from guile, cunning, or deceit; simplicity or artlessness.
Plural form of innocent.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition, from Wiktionary, Creative Commons Attribution/Share-Alike License and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.
If they are spelled the same then they are also homographs (and homonyms); if they are spelled differently then they are also heterographs (literally "different writing").