Class Parent
  {
    List<Son> _SonList =new List<Son>();
    public List<Son> SonList
    {
      get;
    }
   }
   
  Class Son
  {
    Parent _Parent;
    public Parent
    {
       get;
       set;
    }
    string _Data;
    public String Data
    {
      get;set;
    }

    public Son(Parent p, string data)
    {
      _Parent =p;
      _Data=data;
      _Parent.SonList.add(this);
     } 
  }

------解决方案--------------------
public Child_A{}
public Child_B{}
public Parent{
   public Collection<Child_A> Child_As {get;set;}
   public Collection<Child_B> Child_Bs{get;set;}
   }