C# - How To Return Json From Action Method With Array Property

I am trying to return some data as json from an action method.

I have an employee object that looks like this:

public class Employee
{
public int EmployeeID {get; set;}
public string FirstName {get; set;}
public string LastName {get; set;}
//Other irrelevant properties
}

Then I have a view model as follows

public Class EmployeeViewModel
{
public Employee Supervisor{get; set;}
public List<EmployeeViewModel> Employees
}

I need to return a json object that looks exactly like this:

{id: 1, name: John, children: [
{id: 1, name: Joe, children: []},
{id: 1, name: Rob, children: []}
]}

For now I only need to go to the second level as above, returning and supervisor and their staff members beneath them.

How would I go about returning this in my action method(I have the viewModel object hydrated already I just need to return it as json). My problem so far has been that the children property does not get populated.