Сircumvent the limitation of c# and pass collection of child elements

In my Windows Store App I used c# 5.0. And I need to call the method which takes collection of base class, by passing collection of child class:

    public class Foo // base class
    {
         public int fooVariable = 1;
         public void fooMethod(){....};  
    }
    public class Bar:Foo // child class

    public void DoSomething(Foo foo)
    public void DoSomething(List<Foo> foos)
    {
        foreach (var foo in foos)
        {
            Debug.WriteLine(foo.i);  //access to variable
            foo.fooMethod();         //access to method
            foo.i = 10;              //!!!i can change variable!!!
        }
    }

    private List<Bar> _list;
    public void Call()
    {
        DoSomething(new Bar());         // ok
        _list = new List<Bar>();
        list.Add(new Bar());            // I can add a lot of items.
        DoSomething(list);              // not ok

        foreach (var foo in foos)
        {
            Debug.WriteLine(foo.i);  // in console I need to see '10'
        }
    }

Is it possible to circumvent such limitation? If yes - how?

UPD

In DoSomething I neeed full access to all public methods/variables(read/write) /properties(read/write)