this.form = this.fb.group({
  'name':[''],
  'nested': this.fb.group({
    'date':['']
    // ...
  })
});

this.form = this.fb.group({ 'name':[''], 'nested': this.fb.group({ 'date':[''] // ... }) });

<form [formGroup]="form" >
  <input formControlName="name" ... />
  <div formGroupName="nested">
    <input formControlName="date" ... />
  </div>
</form>

<form [formGroup]="form" > <input formControlName="name" ... /> <div formGroupName="nested"> <input formControlName="date" ... /> </div> </form>