When casting annoying kid voices, you should work with kids who have acting experience. Going with an older voice can backfire on you because some people can tell when someone is pretending to be what they’re not. Very few adults can pull off a child’s voice and convince an audience. There is an innocence to a child’s voice that’s merely difficult to imitate. For an annoying voice to come off painfully perfect, the voice actor should know precisely what you imagined in your head
You can target any audience with an annoying child voice because we are all surrounded by kids. What matters, in this case, is the scene you want to set. It could be at home, in school, at the mall, or in the park. Kids are everywhere, and they can decide to be annoying within a blink of an eye.
An annoying child’s voice should be infuriating because it’s not a pleasant experience to go through. You should focus on getting under your audience’s skin.