It's both fun and scary to be a little kid. There's more potential for magic and wonder everywhere you look. But there's also more potential for danger too. In Matilda, it's not just that grown-ups don't take kids seriously, or that they aren't allowed to read through dinner if that's what they want to do. People like the Trunchbull can throw kids around by their hair or lock them up in places like The Chokey. They can tell youngsters that they're wrong or stupid, and they're supposed to sit there and take it. That's part of what makes Matilda awesome. She isn't going to take that stuff from anyone. She'll stand up to any grown-up there is.
The smallest, youngest people in this book, like Matilda, Lavender, and even Nigel, are the wisest. Even though there is a ton of stuff they still don't know, they absolutely know right from wrong, and are determined to see justice done against the Trunchbull.
In spite of how scary the Trunchbull is, nothing she does can keep the kids at Crunchem Hall from acting like the kids they are; in fact, the meaner she is the more determined they are to play pranks and sneak around.