Jan 14, 2008 12:07 AM|Nai-Dong Jin - MSFT|LINK
Just mentioned by Mercury, something like adding child controls would not be recommended to finish in constructor. They should be finished in CreateChildControls method.
Second, as you said that you want to add a compare validator controls. Well, no matter what kind of controls you want to add, you should expose some public properties which links to the properties of compare validator controls. So in this way, The child
control compare validator can community with other objects which is outside of the custom server control.