A simple two way binding example in vue3.

Child.vue:

<script lang="ts" setup>
const name = defineModel<string>('name');
const age = defineModel<number>('age');

const updateAgeInChild = () => {
  ++age.value;
};
</script>

<template>
  <h1>Child: </h1>
  <p>name: {{ name }}</p>
  <p>age: {{ age }}</p>
  <input type="text" v-model="name"/>
  <button @click="updateAgeInChild()">Add age in Child</button>
</template>

Parent.vue:

<script lang="ts" setup>
  import { ref } from 'vue';
  import Child from './Child.vue';

  const name = ref('BlockLune');
  const age = ref(0);

  const updateAgeInParent = () => {
    ++age.value;
  };
</script>

<template>
  <Child v-model:name="name" v-model:age="age" />
  <h1>Parent: </h1>
  <p>name: {{ name }}</p>
  <p>age: {{ age }}</p>
  <input type="text" v-model="name"/>
  <button @click="updateAgeInParent">Add in Parent</button>
</template>

App.vue:

<script setup>
import Parent from './Parent.vue';
</script>

<template>
  <Parent />
</template>

Learn more at Component v-model | Vue.js. Note the Under the Hood part.