Here counter is a child component accessed by demo which is a parent component using v-model.

// child component
Vue.component('counter', {
  template: `<div><button @click='add'>+1</button>
  <button @click='sub'>-1</button>
  <div>this is inside the child component: {{ result }}</div></div>`,
  data () {
    return {
      result: 0
    }
  },
  props: ['value'],
  methods: {
    emitResult () {
      this.$emit('input', this.result)
    },
    add () {
      this.result += 1
      this.emitResult()
    },
    sub () {
      this.result -= 1
      this.emitResult()
    }
  }  
})

This child component will be emitting result each time sub() or add() methods are called.

// parent component
new Vue({
  el: '#demo',
  data () {
    return {
      resultFromChild: null
    }
  }
})

// parent template
<div id='demo'>
  <counter v-model='resultFromChild'></counter>
  This is in parent component {{ resultFromChild }}
</div>

Since v-model is present on the child component, a prop with name value was sent at the same time, there is an input event on the counter which will in turn provide the value from the child component.