why the UI doesn't change in checkbox in flutter?

i tried to make a checkbox for a week in flutter . and because of not writing extra code i made a widget "week" and when i run the code i can see the checkboxes but when i click on them the UI doesn't change ... i expect when i click on a ticked box => the box turns to unticked and vice versa. and this doesn't happen and i don't know what is the problem?? please help me ...please... thank you.

here is my whole code:and this is the UI image

import "package:flutter/services.dart";

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyPage(),
    );
  }
}

class MyPage extends StatefulWidget {
  MyPage({super.key});

  @override
  State<MyPage> createState() => _Example();
}

class _Example extends State<MyPage> {
  bool mon = true;
  bool tue = true;
  bool wed = true;
  bool thu = true;
  bool fri = true;
  bool sat = true;
  bool sun = true;

  Widget week(bool? value, String day) {
    return Padding(
      padding: const EdgeInsets.all(5.0),
      child: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text(day),
            Checkbox(
                value: value,
                onChanged: (bool? new_Value) {
                  setState(() {
                    value = new_Value;
                  });
                }),
          ],
        ),
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: const Text('HDBOOKS'),
        ),
        body: Center(
          child: Row(
            children: [
              week(mon, 'Mon'),
              week(tue, 'Tue'),
              week(wed, 'Wed'),
              week(thu, 'Thu'),
              week(fri, 'fri'),
              week(sat, 'sat'),
              week(sun, 'sun'),
            ],
          ),
        ));
  }
}

... i expect when i click on a ticked box => the box turns to unticked and vice versa. and this doesn't happen and i don't know what is the problem?? please help me ...please... thank you.