MVC Required Property within Optional Property

I have two entities:

public class ParentThing
{
    [Key]
    public int Id { get; set; }

    [Required]
    public ChildThing TheFirstThing { get; set; }

    public ChildThing TheSecondThing { get; set; }
}

public class ChildThing
{
    [Key]
    public int Id { get; set; }

    [Required]
    public string Code { get; set; }

    public string Name { get; set; }
}

and a view model:

public class ParentViewModel
{
    public string Message { get; set; }

    public ParentThing ParentThing { get; set; }
}

and a view:

@using (@Html.BeginForm())
{
    <label>Code 1</label>
    @Html.EditorFor(model => model.ParentThing.TheFirstThing.Code)

    <label>Name 1</label>
    @Html.EditorFor(model => model.ParentThing.TheFirstThing.Name)

    <label>Code 2</label>
    @Html.EditorFor(model => model.ParentThing.TheSecondThing.Code)

    <label>Name 2</label>
    @Html.EditorFor(model => model.ParentThing.TheSecondThing.Name)

    <input type="submit" value="Save" />
}

In my post back I add the ParentThing to the context and attempt to save changes. I receive a validation error on the Code property of the TheSecondThing property of the ParentThing as it is required.

What are some alternatives for saving an optional property that contains required properties?