It's going to be real hard for kids to simply jump from 'wear a mask or Granny or your friends will die' to 'it was all a big lie' or even 'well they just made a mistake.' That was sure one big fat "mistake" that may truly need some counceling to wrap little minds around.
With other big lies like Santa and tooth fairy they at least have time to 'grow' out of it over time till they can grasp it with more developed minds and maturity