Attach a child control on a Custom Control

Question

Hi, I am programming a custom control behaving almost as a GroupBox control. At design time, when I drop another control (say a CheckBox)on this GroupBox, it does not seem to be attached to it. I know I have to call the GroupBox.Controls.Add method, but I do not know where to do that. Using the DragDrop event of the GroupBox, I am not able to find any references of the "being created" CheckBox, in fact, I think that it does not even exist. So what is the solution? Many thanks Christophe.