Outside of being born in a cult, I’m sure the average kid is aware of Japanese as a language by 10, and that’s if they weren’t already being taught the language from 4
You can carry white lies, that you were told at a very young age, with you for many years. There’s loads of stories of people being told some fairytale incorrect information at a young age and then just believing that for years until they suddenly have an epiphany as an adult.