How else can we communicate with the chosen children in such a fashion if we aren't beings within the story? Disembodied voices don't just come from nowhere! We're even tangible to some of the characters, which means there must be some sort of device which communicates our thoughts.
The rainbow snail is just my first guess of where we are. The snail, like us, was with the story to begin with, and, has interacted to both the characters. You may argue that the rainbow snail looks like none of us, but keep in mind that we are legion, who is to say what we look like as a collective, especially in a story where the real form and the true form of people differ so greatly?
I'm just saying, Do Not Trust Yourself.
H͡o̸w͝ éls̛e c͟an͜ ͜we͏ c̸̘͓̊ͥ̾͊͆ͤo͕̦m̙͍̙m̉̂́̿u̎̊͂̀ͪ͏͍̜n͊҉͍̼̼̱͙̦i̩͉̮̱͉̖̠c̪̯a̭̪͚͕̬̭̎͒͡ţ̈́e͇̘͠w̴ith̶ ҉t͢he ch̢os͝e̢n ̴c̵h̵ild͠r͡en i̸n ̶s͘u̴Ch̨̦͙̘͆͆̇̽̀ af̰̻̠̱̼̳̗͕͗̏ͩ̄͂ạ̡̢̲͉̺̫̠͓̪̇͒ͥ̇ͦ͢s͚͈̮̗̳̙̬̞̦ͬ͌̍̅̈͢h̢̨͚̻̖̭̞̅͂ͯ̽ͯį̶̩̲̙ͨ̃ͥ̾ͬ̃̚o̔ͪ̔͏̳̖̹̣̗n̵͈͉̣̯̤̠͒̿̀ ͇̻̤ͫ͋ͯ̇̿́i̧̡͚̲̝̝͕̭̽̅̀̅̽ͦf̧̠͚̮͓̞̞͎͆ͣͣ̽ ̶ͥ̑͆ͮ҉̷̤̦̻̖̰wͯ́̈́̌͏̘͚̀e̯̙̺̫̳̪͆̚͜͜ ̸͍̗͎͍̽ͨͫ̾͑ͧͣ͘ą̟̲͔̰̻͚͓͉̿ͫ̑̽ͣͯ͋̚r̸̨̨̥̳͈̦͓̣͈̊̂ͤ̏̉ͣͭẹ̺̪̠̝̜̖͊͐́n̢͈̟̱̼̦̻͎͐ͫ̽̊̾͑͜ͅ'̊ͦͯ̃͏̛̖̟͖͓͙͚̪̮t̿ͬ͒͆҉̭̩͔̖͖͖ ̸̈́ͮ͜͏̘̯̬̤͕̞̝̲̣b̨̗̬̤̩̠̓͟͠e͍̹͛̏̎̔͛̏ͮ̈i̵̴̦̜̪̘̓̅͋̉̂͐n̷̨̻̘̩̋̌̃ͧ̅ͯͭ̿͞g̋̾҉̞̞̪̙̫s̸̶̡̬̼̣͖͍ͪ́ͭ͑͆ ̨̥̙͍͊ͨ͂ͩ̾͒͢w̉ͨ͏̹̜̜͈̖̞̱į̸̲̹̂ͦ̉ͨ̂ͤ͗́̚͡ṭ̖̩̞̗̬̼͇̅̂̽̈ͨ̅ͫ͆h̗̞͙̬̜͈̗ͪ͐̕ị̮̫͍̣͉̪̐̋ͥͤn̴̸̬̞ͤ͌̽̊̌̈̀ ̯̹͚̙̪̲̳͕͌́̽̎̈̊t̷̼̭̣͕̠͙͍͎̓̑͠h̴̛͚̗̮͉̄͂̈́̀ͣ͌͠e̛̙̖̳͓̮͈̩̰̓ͣ͐ ̴̭̺̜̍͑͂ͮ̏ș̫͋ͧ̀̅͛ͣ̿̐̀̚t͐ͣͦ͋ͦͭ̑ͬ̊҉̗̤̯̦ͅǭ͔͇̯͍̗̹̪͋̏͋͠r͓͇̩̭͚͊͘͠y?