$emit doesn't trigger child events

While the other answers are correct and it is usually possible to use a data driven approach.

I'm going to add this for anyone looking for an answer to this question who need a way other than props. I ran into a similar problem when trying to set focus on a particular input inside a custom form component. To do this I had to give the custom component a ref then do this.

this.$refs.customInput.$emit('focus');
//or
this.$refs.customInput.directlyCallMethod();

This access the vue instance of the child and then you can emit an event that is heard by that component.

As par the documentation:

In Vue.js, the parent-child component relationship can be summarized as props down, events up. The parent passes data down to the child via props, and the child sends messages to the parent via events. Let’s see how they work next.

So in latest Vue, you can not send events from parent to child, you can pass props to child, and send event from child to parent.

You can use a custom Vue instance for that.

// Globally
const eventBus = new Vue()

// In your child
eventBus.$on('eventName', () => {
    // Do something
});

// In your parent
eventBus.$emit('eventName')