Note: The purpose of this video is to briefly demonstrate the essence of the observer pattern.  The resulting code (below) is written for brevity/simplicity and so is not necessarily optimal for production.

public class Parent

{

    public String Name { get; set; }

    public void OnChildCry(Child c)

    {

        Console.WriteLine(this.Name + " heard " + c.Name + " cry");

    }

}

public class Child

{

    public Child()

    {

        Parents = new List<Parent>();

    }

    public String Name { get; set; }

    public List<Parent> Parents { get; set; }

    public void Cry()

    {

        foreach(Parent p in Parents)

            p.OnChildCry(this);

    }

}

class Program

{

    static void Main(string[] args)

    {

        Parent Ralph = new Parent { Name = "Ralph" };

        Child Billy = new Child { Name = "Billy" };

        Parent Mary = new Parent { Name = "Mary" };

        Billy.Parents.Add(Ralph);

        Billy.Parents.Add(Mary);

        Billy.Cry();

        Console.Read();

    }

}