C#

public class Foo
{

   private FooCollection children = new FooCollection();
   
   public Foo()
   {
      children.ItemAdded += SomeDelegate(this.ChildAddedCallback);
   }
   
   private void ChildAddedCallback(Foo addedChild)
   {
   	// do something special
   }
      
   public FooCollection Children
   {
      get
      {
      	return this.children;
      }
   }
}

<pre>public class FooCollection
{
   public event SomeDelegate ItemAdded;
   
   public FooCollection()
   {
   }
   
   public void Add(Foo item)
   {
   	if(this.ItemAdded != null)
   	   this.ItemAdded(item);
   }
}

// adding a child to the control
FooBarControl.Children.Add(foo);

// adding a child to the child
foo.Children.Add(anotherFoo);

public class Foo
{
   private FooCollection internalChildren = new FooCollection();
   
   public Foo()
   {
   }
   
   public void AddChild(Foo child)
   {
      internalChildren.Add(child);
      
      // do something special
   }
   
   public FooCollection GetChildren()
   {
   	FooCollection externalChildren = new FooCollection();
   	
   	foreach(Foo child in internalChildren)
   	   externalChildren.Add(child);
   	   
   	return externalChildren;
   }
}

<pre>public class FooCollection
{
   public class FooCollection()
   {
   }
   
   public void Add(Foo item)
   {
   }
}

// adding a child to the control
FooBarControl.AddChild(foo);

// adding a child to the child
foo.AddChild(anotherFoo); // note that Foo.AddChild is a different method than FooBarControl.AddChild