class Ctrl...
{
...
     bool owned : 1;
....
protected:
    bool IsOwned()const{ return owned; }
    Ctrl& Owned(bool v){ owned=v; return *this; }

public:
    template <typename ChildType>
    ChildType& AddOwned()
    {
        ChildType* p=new ChildType();
        p->Owned();
        (void)Add(p);
        return *p;
    }


    template <typename ChildType, typename T>
    ChildType& AddOwned(T& t)
    {
        ChildType* p=new ChildType(t);
        p->Owned();
        (void)Add(p);
        return *p;
    }

    // return ChildType so that user can further set its
    // properties.

    // The IsOwned and Owned functions will be demoted to protected
    // so that they are available only to libary developers
    //
    // whether a child is owned is a one time decision.
    // an owned child will not be able to be reverted to unowned
    // by end user (without derive from the Ctrl class or its 
    // derivatives), but he/she is free to change parents for it
    //
    // Unless the end user uses some hackish practice,
    // library developers can be assured the owned flag
    // is reliable and predictable. 
};