Angular Two-Way Data Binding and Watching for Changes in Parent Component

It seems there is no way to watch changes in the parent component when using two-way data binding.

I have a custom input component for collecting a tag list. Two-way data binding is setup and working between this component and its parent.

// the parent component is just a form
// here is how I'm adding the child component
<input-tags formControlName="skillField" [(tags)]='skillTags' (ngModelChange)="skillTagUpdate($event)"></input-tags>

In the parent component how do you watch the bound variable for changes? While it's always up to date (I've confirmed this) I cannot find any guidance on reacting to changes.

I've tried:

ngOnChanges(changes: SimpleChanges) {
    if (changes['skillTags']) {
        console.log(this.skillTags);  // nothing
    }
}

and

skillTagUpdate(event){
    console.log(event); // nothing
}

from Angular Two-Way Data Binding and Watching for Changes in Parent Component