Why does Joetta think Kenny has changed his clothes? Chapter 14 The Watsons go to Birmingham
It appears that Joetta (or Joey) thinks that Kenny is trying to scare her. She thinks that he is trying to hide something from her. Specifically, it looks like she believes that he is trying to hide something about their mom and dad from her.
She thinks that Kenny is trying to mess with her mind. She believes that she saw him across the street just a moment ago but that he was wearing different clothes. So she is sure that he has somehow managed to sneak in and change clothes just to spook her.