describeChildren() {
    return this.children
  }
Return the descriptor(s) for the actual children to be created and managed. By default
this simply returns the value of the `children` property set by the parent, but you can
override it to customize how the child content should be structured, for instance to wrap
the `children` within a deeper structure, add in anonymous child siblings, or modify the
`children` configurations.
@protected
@return {FacadeDescriptor | Array<FacadeDescriptor>}